sdc - SDC Parent Project Catalog FE and BE

Age	Commit message (Expand)	Author	Files	Lines
2017-10-04	Merge "New docker start monitor engine"	Michael Lando	1	-0/+1
2017-10-03	Remove icon from sanity tests report	Yuli Shlosberg	1	-7/+2
2017-10-03	New docker start monitor engine	Yuli Shlosberg	1	-0/+1
2017-10-03	Add VNFs to sanity docker	Yuli Shlosberg	1	-18/+12
2017-09-20	Build sanity docker execute automation	Yuli Shlosberg	6	-56/+57
2017-09-13	ComponentBaseTest.java enhancement and	Idan Amit	32	-194/+2854
2017-08-10	[SDC] code sync	Michael Lando	3	-11/+22
2017-08-07	[sdc] sync	Tal Gitelman	1	-6/+28
2017-08-07	[SDC] code sync	Michael Lando	6	-1042/+986
2017-08-02	[SDC] code rebase for sdc resync to LF	Avi Ziv	5	-15/+17
2017-07-17	[SDC] rebase 1710 code	Michael Lando	21	-378/+394
2017-07-16	[sdc] - merged 1707_build into sdc LF	Idan Amit	2	-8/+10
2017-07-03	[sdc] - last merges before moving to LF	Tal Gitelman	1	-1/+1
2017-07-02	[sdc] - latest swagger, dependencies, tests fix	Tal Gitelman	1	-1/+0
2017-06-29	[SDC] rebase code	Tal Gitelman	6	-44/+75
2017-06-19	[sdc] update to the current code base	Michael Lando	2	-3/+3
2017-06-18	[sdc] update code of sdc	Michael Lando	4	-33/+41
2017-06-11	[SDC-29] rebase continue work to align source	Michael Lando	501	-0/+119040
'>359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133
.. This work is licensed under a Creative Commons Attribution 4.0 International License.
.. http://creativecommons.org/licenses/by/4.0


APEX Policy Guide
*****************************

.. contents::
    :depth: 3

APEX Policy Matrix
^^^^^^^^^^^^^^^^^^

APEX Policy Matrix
------------------

            .. container:: paragraph

               APEX offers a lot of flexibility for defining, deploying,
               and executing policies. Based on a theoretic model, it
               supports virtually any policy model and allows to
               translate legacy policies into the APEX execution format.
               However, the most important aspect for using APEX is to
               decide what policy is needed, what underlying policy
               concepts should be used, and how the decision logic
               should be realized. Once these aspects are decided, APEX
               can be used to execute the policies. If the policy
               evolves, say from a simple decision table to a fully
               adaptable policy, only the policy definition requires
               change. APEX supports all of that.

            .. container:: paragraph

               The figure below shows a (non-exhaustive) matrix, which
               will help to decide what policy is required to solve your
               problem. Read the matrix from left to right choosing one
               cell in each column.

            .. container:: imageblock

               .. container:: content

                  |APEX Policy Matrix|

               .. container:: title

                  Figure 1. APEX Policy Matrix

            .. container:: paragraph

               The policy can support one of a number of stimuli with an
               associated purpose/model of the policy, for instance:

            .. container:: ulist

               -  Configuration, i.e. what should happen. An example is
                  an event that states an intended network configuration
                  and the policy should provide the detailed actions for
                  it. The policy can be realized for instance as an
                  obligation policy, a promise or an intent.

               -  Report, i.e. something did happen. An example is an
                  event about an error or fault and the policy needs to
                  repair that problem. The policy would usually be an
                  obligation, utility function, or goal policy.

               -  Monitoring, i.e. something does happen. An example is
                  a notification about certain network conditions, to
                  which the policy might (or might not) react. The
                  policy will mitigate the monitored events or permit
                  (deny) related actions as an obligation or
                  authorization.

               -  Analysis, i.e. why did something happen. An example is
                  an analytic component sends insights of a situation
                  requiring a policy to act on it. The policy can solve
                  the problem, escalate it, or delegate it as a refrain
                  or delegation policy.

               -  Prediction, i.e. what will happen next. An example are
                  events that a policy uses to predict a future network
                  condition. The policy can prevent or enforce the
                  prediction as an adaptive policy, a utility function,
                  or a goal.

               -  Feedback, i.e. why did something happen or not happen.
                  Similar to analysis, but here the feedback will be in
                  the input event and the policy needs to something with
                  that information. Feedback can be related to history
                  or experience, for instance a previous policy
                  execution. The policy needs to be context-aware or be
                  a meta-policy.

            .. container:: paragraph

               Once the purpose of the policy is decided, the next step
               is to look into what context information the policy will
               require to do its job. This can range from very simple to
               a lot of different information, for instance:

            .. container:: ulist

               -  No context, nothing but a trigger event, e.g. a string
                  or a number, is required

               -  Event context, the incoming event provides all
                  information (more than a string or number) for the
                  policy

               -  Policy context (read only), the policy has access to
                  additional information related to its class but cannot
                  change/alter them

               -  Policy context (read and write), the policy has access
                  to additional information related to its class and can
                  alter this information (for instance to record
                  historic information)

               -  Global context (read only), the policy has access to
                  additional information of any kind but cannot
                  change/alter them

               -  Global context (read and write), the policy the policy
                  has access to additional information of any kind and
                  can alter this information (for instance to record
                  historic information)

            .. container:: paragraph

               The next step is to decide how the policy should do its
               job, i.e. what flavor it has, how many states are needed,
               and how many tasks. There are many possible combinations,
               for instance:

            .. container:: ulist

               -  Simple / God: a simple policy with 1 state and 1 task,
                  which is doing everything for the decision-making.
                  This is the ideal policy for simple situation, e.g.
                  deciding on configuration parameters or simple access
                  control.

               -  Simple sequence: a simple policy with a number of
                  states each having a single task. This is a very good
                  policy for simple decision-making with different
                  steps. For instance, a classic action policy (ECA)
                  would have 3 states (E, C, and A) with some logic (1
                  task) in each state.

               -  Simple selective: a policy with 1 state but more than
                  one task. Here, the appropriate task (and it’s logic)
                  will be selected at execution time. This policy is
                  very good for dealing with similar (or the same)
                  situation in different contexts. For instance, the
                  tasks can be related to available external software,
                  or to current work load on the compute node, or to
                  time of day.

               -  Selective: any number of states having any number of
                  tasks (usually more than 1 task). This is a
                  combination of the two policies above, for instance an
                  ECA policy with more than one task in E, C, and A.

               -  Classic directed: a policy with more than one state,
                  each having one task, but a non-sequential execution.
                  This means that the sequence of the states is not
                  pre-defined in the policy (as would be for all cases
                  above) but calculated at runtime. This can be good to
                  realize decision trees based on contextual
                  information.

               -  Super Adaptive: using the full potential of the APEX
                  policy model, states and tasks and state execution are
                  fully flexible and calculated at runtime (per policy
                  execution). This policy is very close to a general
                  programming system (with only a few limitations), but
                  can solve very hard problems.

            .. container:: paragraph

               The final step is to select a response that the policy
               creates. Possible responses have been discussed in the
               literature for a very long time. A few examples are:

            .. container:: ulist

               -  Obligation (deontic for what should happen)

               -  Authorization (e.g. for rule-based or other access
                  control or security systems)

               -  Intent (instead of providing detailed actions the
                  response is an intent statement and a further system
                  processes that)

               -  Delegation (hand the problem over to someone else,
                  possibly with some information or instructions)

               -  Fail / Error (the policy has encountered a problem,
                  and reports it)

               -  Feedback (why did the policy make a certain decision)

APEX Policy Model
^^^^^^^^^^^^^^^^^

Introduction
------------

            .. container:: paragraph

               The APEX policy model is shown in UML notation in the
               figure below. A policy model can be stored in JSON or XML
               format in a file or can be held in a database. The APEX
               editor creates and modifies APEX policy models. APEX
               deployment deploys policy models, and a policy model is
               loaded into APEX engines so that the engines can run the
               policies in the policy model.

            .. container:: paragraph

               The figure shows four different views of the policy
               model:

            .. container:: ulist

               -  The general model view shows the main parts of a
                  policy: state, state output, event, and task. A task
                  can also have parameters. Data types can be defined on
                  a per-model basis using either standard atomic types
                  (such as character, string, numbers) or complex types
                  from a policy domain.

               -  The logic model view emphasizes how decision-making
                  logic is injected into a policy. There are essentially
                  three different types of logic: task logic (for
                  decision making in a task), task selection logic (to
                  select a task if more than one is defined in a state),
                  and state finalizer logic (to compute the final output
                  event of a state and select an appropriate next state
                  from the policy model).

               -  The context model view shows how context is injected
                  into a policy. States collect all context from their
                  tasks. A task can define what context it requires for
                  the decision making, i.e. what context the task logic
                  will process. Context itself is a collection of items
                  (individual context information) with data types.
                  Context can be templated.

               -  The event and field model view shows the events in the
                  policy model. Tasks define what information they
                  consume (input) and produce (output). This information
                  is modeled as fields, essentially a key/type tuple in
                  the model and a key/type/value triple at execution.
                  Events then are collection of fields.

            .. container:: imageblock

               .. container:: content

                  |APEX Policy Model for Execution|

               .. container:: title

                  Figure 2. APEX Policy Model for Execution

Concepts and Keys
#################

               .. container:: paragraph

                  Each element of the policy model is called a
                  *concept*. Each *concept* is a subclass of the
                  abstract *Concept* class, as shown in the next figure.
                  Every concept implements the following abstract
                  methods:

               .. container:: imageblock

                  .. container:: content

                     |Concepts and Keys|

                  .. container:: title

                     Figure 3. Concepts and Keys

               .. container:: ulist

                  -  ``getKey()`` - gets the unique key for this concept
                     instance in the system

                  -  ``validate()`` - validates the structure of this
                     concept, its sub-concepts and its relationships

                  -  ``clean()`` - carries out housekeeping on the
                     concept such as trimming strings, remove any
                     hanging references

                  -  ``clone()`` - creates a deep copy of an instance of
                     this concept

                  -  ``equals()`` - checks if two instances of this
                     concept are equal

                  -  ``toString()`` - returns a string representation of
                     the concept

                  -  ``hashCode()`` - returns a hash code for the
                     concept

                  -  ``copyTo()`` - carries out a deep copy of one
                     instance of the concept to another instance,
                     overwriting the target fields.

               .. container:: paragraph

                  All concepts must have a *key*, which uniquely
                  identifies a concept instance. The *key* of a subclass
                  of an *Concept* must either be an ``ArtifactKey`` or
                  an ``ReferenceKey``. Concepts that have a stand-alone
                  independent existence such as *Policy*, *Task*, and
                  *Event* must have an ``ArtifctKey`` key. Concepts that
                  are contained in other concepts, that do not exist as
                  stand-alone concepts must have an ``ReferenceKey``
                  key. Examples of such concepts are *State* and
                  *EventParameter*.

               .. container:: paragraph

                  An ``ArticactKey`` has two fields; the *Name* of the
                  concept it is the key for and the concept’s *Version*.
                  A concept’s name must be unique in a given
                  PolicyModel. A concept version is represented using
                  the well known *major.minor.path* scheme as used in
                  semantic versioning.

               .. container:: paragraph

                  A ``ReferenceKey`` has three fields. The *UserKeyName*
                  and *UserKeyVersion* fields identify the
                  ``ArtifactKey`` of the concept in which the concept
                  keyed by the ``ReferenceKey`` is contained. The
                  *LocalName* field identifies the contained concept
                  instance. The *LocalName* must be unique in the
                  concepts of a given type contained by a parent.

               .. container:: paragraph

                  For example, a policy called ``SalesPolicy`` with a
                  Version of ``1.12.4`` has a state called ``Decide``.
                  The ``Decide`` state is linked to the ``SalesPolicy``
                  with a ``ReferenceKey`` with fields *UserKeyName* of
                  ``SalesPolicy``, *UserKeyVersion* of ``1.12.4``, and
                  *LocalName* of ``Decide``. There must not be another
                  state called ``Decide`` in the policy ``SalesPolicy``.
                  However, there may well be a state called ``Decide``
                  in some other policy called ``PurchasingPolicy``.

               .. container:: paragraph

                  Each concept in the model is also a JPA (`Java
                  Persistence
                  API <https://en.wikipedia.org/wiki/Java_Persistence_API>`__)
                  Entity. This means that every concept can be
                  individually persisted or the entire model can be
                  persisted en-bloc to any persistence mechanism using
                  an JPA framework such as
                  `Hibernate <http://hibernate.org/>`__ or
                  `EclipseLink <http://www.eclipse.org/eclipselink/>`__.

Concept: PolicyModel
####################

               .. container:: paragraph

                  The *PolicyModel* concept is a container that holds
                  the definition of a set of policies and their
                  associated events, context maps, and tasks. A
                  *PolicyModel* is implemented as four maps for
                  policies, events, context maps, and tasks. Each map is
                  indexed by the key of the policy, event, context map,
                  or task. Any non-empty policy model must have at least
                  one entry in its policy, event, and task map because
                  all policies must have at least one input and output
                  event and must execute at least one task.

               .. container:: paragraph

                  A *PolicyModel* concept is keyed with an
                  ``ArtifactKey key``. Because a *PolicyModel* is an
                  ``AxConcept``, calling the ``validate()`` method on a
                  policy model validates the concepts, structure, and
                  relationships of the entire policy model.

Concept: DataType
#################

               .. container:: paragraph

                  Data types are tightly controlled in APEX in order to
                  provide a very high degree of consistency in policies
                  and to facilitate tracking of changes to context as
                  policies execute. All context is modeled as a
                  *DataType* concept. Each DataType concept instance is
                  keyed with an ``ArtifactKey`` key. The DataType field
                  identifies the Java class of objects that is used to
                  represent concept instances that use this data type.
                  All context has a *DataType*; incoming and outgoing
                  context is represented by *EventField* concepts and
                  all other context is represented by *ContextItem*
                  concepts.

Concept: Event
##############

               .. container:: paragraph

                  An *Event* defines the structure of a message that
                  passes into or out of an APEX engine or that passes
                  between two states in an APEX engine. APEX supports
                  message reception and sending in many formats and all
                  messages are translated into an *Event* prior to
                  processing by an APEX engine. Event concepts are keyed
                  with an ``ArtifactKey`` key. The parameters of an
                  event are held as a map of *EventField* concept
                  instances with each parameter indexed by the
                  *LocalName* of its ``ReferenceKey``. An *Event* has
                  three fields:

               .. container:: ulist

                  -  The *NameSpace* identifies the domain of
                     application of the event

                  -  The *Source* of the event identifies the system
                     that emitted the event

                  -  The *Target* of the event identifies the system
                     that the event was sent to

               .. container:: paragraph

                  A *PolicyModel* contains a map of all the events known
                  to a given policy model. Although an empty model may
                  have no events in its event map, any sane policy model
                  must have at least one *Event* defined.

Concept: EventField
###################

               .. container:: paragraph

                  The incoming context and outgoing context of an event
                  are the fields of the event. Each field representing a
                  single piece of incoming or outgoing context. Each
                  field of an *Event* is represented by an instance of
                  the *EventField* concept. Each *EventField* concept
                  instance in an event is keyed with a ``ReferenceKey``
                  key, which references the event. The *LocalName* field
                  of the ``ReferenceKey`` holds the name of the field A
                  reference to a *DataType* concept defines the data
                  type that values of this parameter have at run time.

Concept: ContextMap
###################

               .. container:: paragraph

                  The set of context that is available for use by the
                  policies of a *PolicyModel* is defined as *ContextMap*
                  concept instances. The *PolicyModel* holds a map of
                  all the *ContextMap* definitions. A *ContextMap* is
                  itself a container for a group of related context
                  items, each of which is represented by a *ContextItem*
                  concept instance. *ContextMap* concepts are keyed with
                  an ``ArtifactKey`` key. A developer can use the APEX
                  Policy Editor to create context maps for their
                  application domain.

               .. container:: paragraph

                  A *ContextMap* uses a map to hold the context items.
                  The ContextItem concept instances in the map are
                  indexed by the *LocalName* of their ``ReferenceKey``.

               .. container:: paragraph

                  The *ContextMapType* field of a *ContextMap* defines
                  the type of a context map. The type can have either of
                  two values:

               .. container:: ulist

                  -  A *BAG* context map is a context map with fixed
                     content. Each possible context item in the context
                     map is defined at design time and is held in the
                     *ContextMap* context instance as *ContextItem*
                     concept definitions and only the values of the
                     context items in the context map can be changed at
                     run time. The context items in a *BAG* context map
                     have mixed types and distinct *ContextItem* concept
                     instances of the same type can be defined. A *BAG*
                     context map is convenient for defining a group of
                     context items that are diverse but are related by
                     domain, such as the characteristics of a device. A
                     fully defined *BAG* context map has a fully
                     populated *ContextItem* map but its
                     *ContextItemTemplate* reference is not defined.

                  -  A *SAMETYPE* context map is used to represent a
                     group of *ContextItem* instances of the same type.
                     Unlike a *BAG* context map, the *ContextItem*
                     concept instances of a *SAMETYPE* context map can
                     be added, modified, and deleted at runtime. All
                     *ContextItem* concept instances in a *SAMETYPE*
                     context map must be of the same type, and that
                     context item is defined as a single
                     *ContextItemTemplate* concept instances at design
                     time. At run time, the *ContextItemTemplate*
                     definition is used to create new *ContextItem*
                     concept instances for the context map on demand. A
                     fully defined *SAMETYPE context map has an empty
                     ContextItem map and its ContextItemTemplate\_*
                     reference is defined.

               .. container:: paragraph

                  The *Scope* of a *ContextMap* defines the range of
                  applicability of a context map in APEX. The following
                  scopes of applicability are defined:

               .. container:: ulist

                  -  *EPHEMERAL* scope means that the context map is
                     owned, used, and modified by a single application,
                     but the context map only exists while that
                     application is running

                  -  *APPLICATION* scope specifies that the context map
                     is owned, used, and modified by a single
                     application, the context map is persistent

                  -  *GLOBAL* scope specifies that the context map is
                     globally owned and is used and modified by any
                     application, the context map is persistent

                  -  *EXTERNAL* scope specifies that the context map is
                     owned by an external system and may be used in a
                     read-only manner by any application, the context
                     map is persistent

               .. container:: paragraph

                  A much more sophisticated scoping mechanism for
                  context maps is envisaged for Apex in future work. In
                  such a mechanism, the scope of a context map would
                  work somewhat like the way roles work in security
                  authentication systems.

Concept: ContextItem
####################

               .. container:: paragraph

                  Each piece of context in a *ContextMap* is represented
                  by an instance of the *ContextItem* concept. Each
                  *ContextItem* concept instance in a context map keyed
                  with a ``ReferenceKey`` key, which references the
                  context map of the context item. The *LocalName* field
                  of the ``ReferenceKey`` holds the name of the context
                  item in the context map A reference to a *DataType*
                  concept defines the data type that values of this
                  context item have at run time. The *WritableFlag*
                  indicates if the context item is read only or
                  read-write at run time.

Concept: ContextItemTemplate
############################

               .. container:: paragraph

                  In a *SAMETYPE* *ContextMap*, the
                  *ContextItemTemplate* definition provides a template
                  for the *ContextItem* instances that will be created
                  on the context map at run time. Each *ContextItem*
                  concept instance in the context map is created using
                  the *ContextItemTemplate* template. It is keyed with a
                  ``ReferenceKey`` key, which references the context map
                  of the context item. The *LocalName* field of the
                  ``ReferenceKey``, supplied by the creator of the
                  context item at run time, holds the name of the
                  context item in the context map. A reference to a
                  *DataType* concept defines the data type that values
                  of this context item have at run time. The
                  *WritableFlag* indicates if the context item is read
                  only or read-write at run time.

Concept: Task
#############

               .. container:: paragraph

                  The smallest unit of logic in a policy is a *Task*. A
                  task encapsulates a single atomic unit of logic, and
                  is designed to be a single indivisible unit of
                  execution. A task may be invoked by a single policy or
                  by many policies. A task has a single trigger event,
                  which is sent to the task when it is invoked. Tasks
                  emit one or more outgoing events, which carry the
                  result of the task execution. Tasks may use or modify
                  context as they execute.

               .. container:: paragraph

                  The Task concept definition captures the definition of
                  an APEX task. Task concepts are keyed with an
                  ``ArtifactKey`` key. The Trigger of the task is a
                  reference to the *Event* concept that triggers the
                  task. The *OutgoingEvents* of a task are a set of
                  references to *Event* concepts that may be emitted by
                  the task.

               .. container:: paragraph

                  All tasks have logic, some code that is programmed to
                  execute the work of the task. The *Logic* concept of
                  the task holds the definition of that logic.

               .. container:: paragraph

                  The *Task* definition holds a set of *ContextItem* and
                  *ContextItemTemplate* context items that the task is
                  allow to access, as defined by the task developer at
                  design time. The type of access (read-only or read
                  write) that a task has is determined by the
                  *WritableFlag* flag on the individual context item
                  definitions. At run time, a task may only access the
                  context items specified in its context item set, the
                  APEX engine makes only the context items in the task
                  context item set is available to the task.

               .. container:: paragraph

                  A task can be configured with startup parameters. The
                  set of parameters that can be configured on a task are
                  defined as a set of *TaskParameter* concept
                  definitions.

Concept: TaskParameter
######################

               .. container:: paragraph

                  Each configuration parameter of a task are represented
                  as a *Taskparameter* concept keyed with a
                  ``ReferenceKey`` key, which references the task. The
                  *LocalName* field of the ``ReferenceKey`` holds the
                  name of the parameter. The *DefaultValue* field
                  defines the default value that the task parameter is
                  set to. The value of *TaskParameter* instances can be
                  overridden at deployment time by specifying their
                  values in the configuration information passed to APEX
                  engines.

Concept: Logic
##############

               .. container:: paragraph

                  The *Logic* concept instance holds the actual
                  programmed task logic for a task defined in a *Task*
                  concept or the programmed task selection logic for a
                  state defined in a *State* concept. It is keyed with a
                  ``ReferenceKey`` key, which references the task or
                  state that owns the logic. The *LocalName* field of
                  the Logic concept is the name of the logic.

               .. container:: paragraph

                  The *LogicCode* field of a Logic concept definition is
                  a string that holds the program code that is to be
                  executed at run time. The *LogicType* field defines
                  the language of the code. The standard values are the
                  logic languages supported by APEX:
                  `JAVASCRIPT <https://en.wikipedia.org/wiki/JavaScript>`__,
                  `JAVA <https://java.com/en/>`__,
                  `JYTHON <http://www.jython.org/>`__,
                  `JRUBY <http://jruby.org/>`__, or
                  `MVEL <https://en.wikibooks.org/wiki/Transwiki:MVEL_Language_Guide>`__.

               .. container:: paragraph

                  The APEX engine uses the *LogicType* field value to
                  decide which language interpreter to use for a task
                  and then sends the logic defined in the *LogicCode*
                  field to that interpreter.

Concept: Policy
###############

               .. container:: paragraph

                  The *Policy* concept defines a policy in APEX. The
                  definition is rather straightforward. A policy is made
                  up of a set of states with the flavor of the policy
                  determining the structure of the policy states and the
                  first state defining what state in the policy executes
                  first. *Policy* concepts are keyed with an
                  ``ArtifactKey`` key.

               .. container:: paragraph

                  The *PolicyFlavour* of a *Policy* concept specifies
                  the structure that will be used for the states in the
                  policy. A number of commonly used policy patterns are
                  supported as APEX policy flavors. The standard policy
                  flavors are:

               .. container:: ulist

                  -  The *MEDA* flavor supports policies written to the
                     `MEDA policy
                     pattern <https://www.researchgate.net/publication/282576518_Dynamically_Adaptive_Policies_for_Dynamically_Adaptive_Telecommunications_Networks>`__
                     and require a sequence of four states: namely
                     *Match*, *Establish*, *Decide* and *Act*.

                  -  The *OODA* flavor supports policies written to the
                     `OODA loop
                     pattern <https://en.wikipedia.org/wiki/OODA_loop>`__
                     and require a sequence of four states: namely
                     *Observe*, *Orient*, *Decide* and *Act*.

                  -  The *ECA* flavor supports policies written to the
                     `ECA active rule
                     pattern <https://en.wikipedia.org/wiki/Event_condition_action>`__
                     and require a sequence of three states: namely
                     *Event*, *Condition* and *Action*

                  -  The *XACML* flavor supports policies written in
                     `XACML <https://en.wikipedia.org/wiki/XACML>`__ and
                     require a single state: namely *XACML*

                  -  The *FREEFORM* flavor supports policies written in
                     an arbitrary style. A user can define a *FREEFORM*
                     policy as an arbitrarily long chain of states.

               .. container:: paragraph

                  The *FirstState* field of a *Policy* definition is the
                  starting point for execution of a policy. Therefore,
                  the trigger event of the state referenced in the
                  *FirstState* field is also the trigger event for the
                  entire policy.

Concept: State
##############

               .. container:: paragraph

                  The *State* concept represents a phase or a stage in a
                  policy, with a policy being composed of a series of
                  states. Each state has at least one but may have many
                  tasks and, on each run of execution, a state executes
                  one and only one of its tasks. If a state has more
                  than one task, then its task selection logic is used
                  to select which task to execute. Task selection logic
                  is programmable logic provided by the state designer.
                  That logic can use incoming, policy, global, and
                  external context to select which task best
                  accomplishes the purpose of the state in a give
                  situation if more than one task has been specified on
                  a state. A state calls one and only one task when it
                  is executed.

               .. container:: paragraph

                  Each state is triggered by an event, which means that
                  all tasks of a state must also be triggered by that
                  same event. The set of output events for a state is
                  the union of all output events from all tasks for that
                  task. In practice at the moment, because a state can
                  only have a single input event, a state that is not
                  the final state of a policy may only output a single
                  event and all tasks of that state may also only output
                  that single event. In future work, the concept of
                  having a less restrictive trigger pattern will be
                  examined.

               .. container:: paragraph

                  A *State* concept is keyed with a ``ReferenceKey``
                  key, which references the *Policy* concept that owns
                  the state. The *LocalName* field of the
                  ``ReferenceKey`` holds the name of the state. As a
                  state is part of a chain of states, the *NextState*
                  field of a state holds the ``ReferenceKey`` key of the
                  state in the policy to execute after this state.

               .. container:: paragraph

                  The *Trigger* field of a state holds the
                  ``ArtifactKey`` of the event that triggers this state.
                  The *OutgoingEvents* field holds the ``ArtifactKey``
                  references of all possible events that may be output
                  from the state. This is a set that is the union of all
                  output events of all tasks of the state.

               .. container:: paragraph

                  The *Task* concepts that hold the definitions of the
                  task for the state are held as a set of
                  ``ArtifactKey`` references in the state. The
                  *DefaultTask* field holds a reference to the default
                  task for the state, a task that is executed if no task
                  selection logic is specified. If the state has only
                  one task, that task is the default task.

               .. container:: paragraph

                  The *Logic* concept referenced by a state holds the
                  task selection logic for a state. The task selection
                  logic uses the incoming context (parameters of the
                  incoming event) and other context to determine the
                  best task to use to execute its goals. The state holds
                  a set of references to *ContextItem* and
                  *ContextItemTemplate* definitions for the context used
                  by its task selection logic.

Writing Logic
^^^^^^^^^^^^^

Writing APEX Task Logic
-----------------------

            .. container:: paragraph

               Task logic specifies the behavior of an Apex Task. This
               logic can be specified in a number of ways, exploiting
               Apex’s plug-in architecture to support a range of logic
               executors. In Apex scripted Task Logic can be written in
               any of these languages:

            .. container:: ulist

               -  ```MVEL`` <https://en.wikipedia.org/wiki/MVEL>`__,

               -  ```JavaScript`` <https://en.wikipedia.org/wiki/JavaScript>`__,

               -  ```JRuby`` <https://en.wikipedia.org/wiki/JRuby>`__ or

               -  ```Jython`` <https://en.wikipedia.org/wiki/Jython>`__.

            .. container:: paragraph

               These languages were chosen because the scripts can be
               compiled into Java bytecode at runtime and then
               efficiently executed natively in the JVM. Task Logic an
               also be written directly in Java but needs to be
               compiled, with the resulting classes added to the
               classpath. There are also a number of other Task Logic
               types (e.g. Fuzzy Logic), but these are not supported as
               yet. This guide will focus on the scripted Task Logic
               approaches, with MVEL and JavaScript being our favorite
               languages. In particular this guide will focus on the
               Apex aspects of the scripts. However, this guide does not
               attempt to teach you about the scripting languages
               themselves … that is up to you!

            .. tip::  
			   JVM-based scripting languages
			   For more more information on scripting for the Java platform see: https://docs.oracle.com/javase/8/docs/technotes/guides/scripting/prog_guide/index.html

            .. note:: 
			   What do Tasks do?
			   The function of an Apex Task is to provide the logic that can be executed for an Apex State as one of the steps in
			   an Apex Policy. Each task receives some *incoming fields*, executes some logic (e.g: make a decision based on
			   *shared state* or *context*, *incoming fields*, *external context*, etc.), perhaps set some *shared state* or 
			   *context* and then emits *outgoing fields*. The state that uses the task is responsible for extracting the
			   *incoming fields* from the state input event. The state also has an *output mapper* associated with the task, and
			   this *output mapper* is responsible for mapping the *outgoing fields* from the task into an appropriate
			   output event for the state.

            .. container:: paragraph

               First lets start with a sample task, drawn from the "My
               First Apex Policy" example: The task "MorningBoozeCheck"
               from the "My First Apex Policy" example is available in
               both MVEL and JavaScript:

            .. container:: listingblock

               .. container:: title

                  Javascript code for the ``MorningBoozeCheck`` task

               .. container:: content

                  .. code:: javascript
                     :number-lines:

                     /*
                      * ============LICENSE_START=======================================================
                      *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
                      * ================================================================================
                      * Licensed under the Apache License, Version 2.0 (the "License");
                      * you may not use this file except in compliance with the License.
                      * You may obtain a copy of the License at
                      *
                      *      http://www.apache.org/licenses/LICENSE-2.0
                      *
                      * Unless required by applicable law or agreed to in writing, software
                      * distributed under the License is distributed on an "AS IS" BASIS,
                      * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
                      * See the License for the specific language governing permissions and
                      * limitations under the License.
                      *
                      * SPDX-License-Identifier: Apache-2.0
                      * ============LICENSE_END=========================================================
                      */

                     var returnValueType = Java.type("java.lang.Boolean");
                     var returnValue = new returnValueType(true);

                     // Load compatibility script for imports etc
                     load("nashorn:mozilla_compat.js");
                     importPackage(java.text);
                     importClass(java.text.SimpleDateFormat);

                     executor.logger.info("Task Execution: '"+executor.subject.id+"'. Input Fields: '"+executor.inFields+"'");

                     executor.outFields.put("amount"      , executor.inFields.get("amount"));
                     executor.outFields.put("assistant_ID", executor.inFields.get("assistant_ID"));
                     executor.outFields.put("notes"       , executor.inFields.get("notes"));
                     executor.outFields.put("quantity"    , executor.inFields.get("quantity"));
                     executor.outFields.put("branch_ID"   , executor.inFields.get("branch_ID"));
                     executor.outFields.put("item_ID"     , executor.inFields.get("item_ID"));
                     executor.outFields.put("time"        , executor.inFields.get("time"));
                     executor.outFields.put("sale_ID"     , executor.inFields.get("sale_ID"));

                     item_id = executor.inFields.get("item_ID");

                     //All times in this script are in GMT/UTC since the policy and events assume time is in GMT.
                     var timenow_gmt =  new Date(Number(executor.inFields.get("time")));

                     var midnight_gmt = new Date(Number(executor.inFields.get("time")));
                     midnight_gmt.setUTCHours(0,0,0,0);

                     var eleven30_gmt = new Date(Number(executor.inFields.get("time")));
                     eleven30_gmt.setUTCHours(11,30,0,0);

                     var timeformatter = new java.text.SimpleDateFormat("HH:mm:ss z");

                     var itemisalcohol = false;
                     if(item_id != null && item_id >=1000 && item_id < 2000)
                         itemisalcohol = true;

                     if( itemisalcohol
                         && timenow_gmt.getTime() >= midnight_gmt.getTime()
                         && timenow_gmt.getTime() <  eleven30_gmt.getTime()) {

                       executor.outFields.put("authorised", false);
                       executor.outFields.put("message", "Sale not authorised by policy task " +
                         executor.subject.taskName+ " for time " + timeformatter.format(timenow_gmt.getTime()) +
                         ". Alcohol can not be sold between " + timeformatter.format(midnight_gmt.getTime()) +
                         " and " + timeformatter.format(eleven30_gmt.getTime()));
                     }
                     else{
                       executor.outFields.put("authorised", true);
                       executor.outFields.put("message", "Sale authorised by policy task " +
                         executor.subject.taskName + " for time "+timeformatter.format(timenow_gmt.getTime()));
                     }

                     /*
                     This task checks if a sale request is for an item that is an alcoholic drink.
                     If the local time is between 00:00:00 GMT and 11:30:00 GMT then the sale is not
                     authorised. Otherwise the sale is authorised.
                     In this implementation we assume that items with item_ID value between 1000 and
                     2000 are all alcoholic drinks :-)
                     */

            .. container:: listingblock

               .. container:: title

                  MVEL code for the ``MorningBoozeCheck`` task

               .. container:: content

                  .. code:: javascript 
                     :number-lines:

                     /*
                      * ============LICENSE_START=======================================================
                      *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
                      * ================================================================================
                      * Licensed under the Apache License, Version 2.0 (the "License");
                      * you may not use this file except in compliance with the License.
                      * You may obtain a copy of the License at
                      *
                      *      http://www.apache.org/licenses/LICENSE-2.0
                      *
                      * Unless required by applicable law or agreed to in writing, software
                      * distributed under the License is distributed on an "AS IS" BASIS,
                      * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
                      * See the License for the specific language governing permissions and
                      * limitations under the License.
                      *
                      * SPDX-License-Identifier: Apache-2.0
                      * ============LICENSE_END=========================================================
                      */
                     import java.util.Date;
                     import java.util.Calendar;
                     import java.util.TimeZone;
                     import java.text.SimpleDateFormat;

                     logger.info("Task Execution: '"+subject.id+"'. Input Fields: '"+inFields+"'");

                     outFields.put("amount"      , inFields.get("amount"));
                     outFields.put("assistant_ID", inFields.get("assistant_ID"));
                     outFields.put("notes"       , inFields.get("notes"));
                     outFields.put("quantity"    , inFields.get("quantity"));
                     outFields.put("branch_ID"   , inFields.get("branch_ID"));
                     outFields.put("item_ID"     , inFields.get("item_ID"));
                     outFields.put("time"        , inFields.get("time"));
                     outFields.put("sale_ID"     , inFields.get("sale_ID"));

                     item_id = inFields.get("item_ID");

                     //The events used later to test this task use GMT timezone!
                     gmt = TimeZone.getTimeZone("GMT");
                     timenow = Calendar.getInstance(gmt);
                     df = new SimpleDateFormat("HH:mm:ss z");
                     df.setTimeZone(gmt);
                     timenow.setTimeInMillis(inFields.get("time"));

                     midnight = timenow.clone();
                     midnight.set(
                         timenow.get(Calendar.YEAR),timenow.get(Calendar.MONTH),
                         timenow.get(Calendar.DATE),0,0,0);
                     eleven30 = timenow.clone();
                     eleven30.set(
                         timenow.get(Calendar.YEAR),timenow.get(Calendar.MONTH),
                         timenow.get(Calendar.DATE),11,30,0);

                     itemisalcohol = false;
                     if(item_id != null && item_id >=1000 && item_id < 2000)
                         itemisalcohol = true;

                     if( itemisalcohol
                         && timenow.after(midnight) && timenow.before(eleven30)){
                       outFields.put("authorised", false);
                       outFields.put("message", "Sale not authorised by policy task "+subject.taskName+
                         " for time "+df.format(timenow.getTime())+
                         ". Alcohol can not be sold between "+df.format(midnight.getTime())+
                         " and "+df.format(eleven30.getTime()));
                       return true;
                     }
                     else{
                       outFields.put("authorised", true);
                       outFields.put("message", "Sale authorised by policy task "+subject.taskName+
                         " for time "+df.format(timenow.getTime()));
                       return true;
                     }

                     /*
                     This task checks if a sale request is for an item that is an alcoholic drink.
                     If the local time is between 00:00:00 GMT and 11:30:00 GMT then the sale is not
                     authorised. Otherwise the sale is authorised.
                     In this implementation we assume that items with item_ID value between 1000 and
                     2000 are all alcoholic drinks :-)
                     */

            .. container:: paragraph

               The role of the task in this simple example is to copy
               the values in the incoming fields into the outgoing
               fields, then examine the values in some incoming fields
               (``item_id`` and ``time``), then set the values in some
               other outgoing fields (``authorised`` and ``message``).

            .. container:: paragraph

               Both MVEL and JavaScript like most JVM-based scripting
               languages can use standard Java libraries to perform
               complex tasks. Towards the top of the scripts you will
               see how to import Java classes and packages to be used
               directly in the logic. Another thing to notice is that
               Task Logic should return a ``java.lang.Boolean`` value
               ``true`` if the logic executed correctly. If the logic
               fails for some reason then ``false`` can be returned, but
               this will cause the policy invoking this task will fail
               and exit.

            .. note::
			   How to return a value from task logic 
			   Some languages explicitly support returning values from the script (e.g. MVEL and JRuby) using an explicit 
			   return statement (e.g. ``return true``), other languages do not (e.g. JavaScript and Jython). For
			   languages that do not support the ``return`` statement, a special field called ``returnValue`` must be
			   created to hold the result of the task logic operation (i.e. assign a ``java.lang.Boolean``
			   value to the ``returnValue`` field before completing the task).
			   Also, in MVEL if there is no explicit return statement then the return value of the last executed statement will return
			   (e.g. the statement a=(1+2) will return the value 3).

            .. container:: paragraph

               Besides these imported classes and normal language
               features Apex provides some natively available parameters
               and functions that can be used directly. At run-time
               these parameters are populated by the Apex execution
               environment and made natively available to logic scripts
               each time the logic script is invoked. (These can be
               accessed using the ``executor`` keyword for most
               languages, or can be accessed directly without the
               ``executor`` keyword in MVEL):

            Table 1. The ``executor`` Fields / Methods
	  
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| Name       | Type        | Java type                      | Description                                                                         |
+============+=============+================================+=====================================================================================+
| inFields   | Fields      | java.util.Map <String,Object>  | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    The incoming task fields. This is implemented as a standard Java                 |
|            |             |                                |    Java (unmodifiable) Map                                                          |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.logger.debug("Incoming fields: "                                  |
|            |             |                                |             +executor.inFields.entrySet());                                         |
|            |             |                                |          var item_id = executor.incomingFields["item_ID"];                          |
|            |             |                                |          if (item_id >=1000) { ... }                                                |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| outFields  | Fields      | java.util.Map <String,Object>  | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    The outgoing task fields. This is implemented as a standard initially empty Java |
|            |             |                                |    (modifiable) Map. To create a new schema-compliant instance of a field object    |
|            |             |                                |    see the utility method subject.getOutFieldSchemaHelper() below                   |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.outFields["authorised"] = false;                                  |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| logger     | Logger      | org.slf4j.ext.XLogger          | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    A helpful logger                                                                 |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.logger.info("Executing task: "                                    |
|            |             |                                |             +executor.subject.id);                                                  |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| TRUE/FALSE | boolean     | java.lang.Boolean              | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    2 helpful constants. These are useful to retrieve correct return  values for the |
|            |             |                                |    task logic                                                                       |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          var returnValue = executor.isTrue;                                         |
|            |             |                                |          var returnValueType = Java.type("java.lang.Boolean");                      |
|            |             |                                |          var returnValue = new returnValueType(true);                               |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| subject    | Task        | TaskFacade                     | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    This provides some useful information about the task that contains this task     |
|            |             |                                |    logic. This object has some useful fields and methods :                          |
|            |             |                                |                                                                                     |
|            |             |                                | .. container:: ulist                                                                |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **AxTask task** to get access to the full task definition of                  |
|            |             |                                |       the host task                                                                 |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **String getTaskName()** to get the name of the host task                     |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **String getId()** to get the ID of the host task                             |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **SchemaHelper getInFieldSchemaHelper( String fieldName )** to                |
|            |             |                                |       get a ``SchemaHelper`` helper object to manipulate incoming                   |
|            |             |                                |       task fields in a schema-aware manner                                          |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **SchemaHelper getOutFieldSchemaHelper( String fieldName )** to               |
|            |             |                                |       get a ``SchemaHelper`` helper object to manipulate outgoing                   |
|            |             |                                |       task fields in a schema-aware manner, e.g. to instantiate new                 |
|            |             |                                |       schema-compliant field objects to populate the                                |
|            |             |                                |       ``executor.outFields`` outgoing fields map                                    |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.logger.info("Task name: "                                         |
|            |             |                                |             +executor.subject.getTaskName());                                       |
|            |             |                                |          executor.logger.info("Task id: "                                           |
|            |             |                                |             +executor.subject.getId());                                             |
|            |             |                                |          executor.logger.info("Task inputs definitions: "                           |
|            |             |                                |             +"executor.subject.task.getInputFieldSet());                            |
|            |             |                                |          executor.logger.info("Task outputs definitions: "                          |
|            |             |                                |             +"executor.subject.task.getOutputFieldSet());                           |
|            |             |                                |          executor.outFields["authorised"] = executor.subject                        |
|            |             |                                |                .getOutFieldSchemaHelper("authorised")                               |
|            |             |                                |               .createNewInstance("false");                                          |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| ContextAlbum getContextAlbum(String ctxtAlbumName )       | .. container:: paragraph                                                            |
|                                                           |                                                                                     |
|                                                           |    A utility method to retrieve a ``ContextAlbum`` for use in the task.             |
|                                                           |    This is how you access the context used by the task. The returned                |
|                                                           |    ``ContextAlbum`` implements the ``java.util.Map <String,Object>``                |
|                                                           |    interface to get and set context as appropriate. The returned                    |
|                                                           |    ``ContextAlbum`` also has methods to lock context albums, get                    |
|                                                           |    information about the schema of the items to be stored in a context              |
|                                                           |    album, and get a ``SchemaHelper`` to manipulate context album items. How         |
|                                                           |    to define and use context in a task is described in the Apex                     |
|                                                           |    Programmer’s Guide and in the My First Apex Policy guide.                        |
|                                                           |                                                                                     |
|                                                           | .. container::                                                                      |
|                                                           |                                                                                     |
|                                                           |    .. container:: content                                                           |
|                                                           |                                                                                     |
|                                                           |       .. container:: paragraph                                                      |
|                                                           |                                                                                     |
|                                                           |          **Example:**                                                               |
|                                                           |                                                                                     |
|                                                           |       .. code:: javascript                                                          |
|                                                           |                                                                                     |
|                                                           |          var bkey = executor.inFields.get("branch_ID");                             |
|                                                           |          var cnts = executor.getContextMap("BranchCounts");                         |
|                                                           |          cnts.lockForWriting(bkey);                                                 |
|                                                           |          cnts.put(bkey, cnts.get(bkey) + 1);                                        |
|                                                           |          cnts.unlockForWriting(bkey);                                               |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+

Writing APEX Task Selection Logic
---------------------------------

   .. container:: paragraph

      The function of Task Selection Logic is to choose which task
      should be executed for an Apex State as one of the steps in an
      Apex Policy. Since each state must define a default task there is
      no need for Task Selection Logic unless the state uses more than
      one task. This logic can be specified in a number of ways,
      exploiting Apex’s plug-in architecture to support a range of logic
      executors. In Apex scripted Task Selection Logic can be written in
      any of these languages:

   .. container:: ulist

      -  ```MVEL`` <https://en.wikipedia.org/wiki/MVEL>`__,

      -  ```JavaScript`` <https://en.wikipedia.org/wiki/JavaScript>`__,

      -  ```JRuby`` <https://en.wikipedia.org/wiki/JRuby>`__ or

      -  ```Jython`` <https://en.wikipedia.org/wiki/Jython>`__.

   .. container:: paragraph

      These languages were chosen because the scripts can be compiled
      into Java bytecode at runtime and then efficiently executed
      natively in the JVM. Task Selection Logic an also be written
      directly in Java but needs to be compiled, with the resulting
      classes added to the classpath. There are also a number of other
      Task Selection Logic types but these are not supported as yet.
      This guide will focus on the scripted Task Selection Logic
      approaches, with MVEL and JavaScript being our favorite languages.
      In particular this guide will focus on the Apex aspects of the
      scripts. However, this guide does not attempt to teach you about
      the scripting languages themselves … that is up to you!

   .. tip::
      JVM-based scripting languages 
	  For more more information on Scripting for the Java platform see:
	  https://docs.oracle.com/javase/8/docs/technotes/guides/scripting/prog_guide/index.html

   .. note::  
      What does Task Selection Logic do? 
	  When an Apex state references multiple tasks, there must be a way to dynamically decide
	  which task should be chosen and executed. This can depend on the many factors, e.g. the
	  *incoming event for the state*, *shared state* or *context*, *external context*,
	  etc.. This is the function of a state’s Task Selection Logic. Obviously, if there is 
	  only one task then Task only one task then Task Selection Logic is not needed. 
	  Each state must also select one of the tasks a the *default state*. If the Task 
	  Selection Logic is unable to select an appropriate task, then it should select the 
	  *default task*. Once the task has been selected the Apex Engine will then execute that
	  task.

   .. container:: paragraph

      First lets start with some simple Task Selection Logic, drawn from
      the "My First Apex Policy" example: The Task Selection Logic from
      the "My First Apex Policy" example is specified in JavaScript
      here:

   .. container:: listingblock

      .. container:: title

         Javascript code for the "My First Policy" Task Selection Logic

      .. container:: content

         .. code:: javascript

            /*
             * ============LICENSE_START=======================================================
             *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
             * ================================================================================
             * Licensed under the Apache License, Version 2.0 (the "License");
             * you may not use this file except in compliance with the License.
             * You may obtain a copy of the License at
             *
             *      http://www.apache.org/licenses/LICENSE-2.0
             *
             * Unless required by applicable law or agreed to in writing, software
             * distributed under the License is distributed on an "AS IS" BASIS,
             * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
             * See the License for the specific language governing permissions and
             * limitations under the License.
             *
             * SPDX-License-Identifier: Apache-2.0
             * ============LICENSE_END=========================================================
             */


            var returnValueType = Java.type("java.lang.Boolean");
            var returnValue = new returnValueType(true);

            executor.logger.info("Task Selection Execution: '"+executor.subject.id+
                "'. Input Event: '"+executor.inFields+"'");

            branchid = executor.inFields.get("branch_ID");
            taskorig = executor.subject.getTaskKey("MorningBoozeCheck");
            taskalt = executor.subject.getTaskKey("MorningBoozeCheckAlt1");
            taskdef = executor.subject.getDefaultTaskKey();

            if(branchid >=0 && branchid <1000){
              taskorig.copyTo(executor.selectedTask);
            }
            else if (branchid >=1000 && branchid <2000){
              taskalt.copyTo(executor.selectedTask);
            }
            else{
              taskdef.copyTo(executor.selectedTask);
            }

            /*
            This task selection logic selects task "MorningBoozeCheck" for branches with
            0<=branch_ID<1000 and selects task "MorningBoozeCheckAlt1" for branches with
            1000<=branch_ID<2000. Otherwise the default task is selected.
            In this case the default task is also "MorningBoozeCheck"
            */

   .. container:: paragraph

      The role of the Task Selection Logic in this simple example is to
      examine the value in one incoming field (``branchid``), then
      depending on that field’s value set the value for the selected
      task to the appropriate task (``MorningBoozeCheck``,
      ``MorningBoozeCheckAlt1``, or the default task).

   .. container:: paragraph

      Another thing to notice is that Task Selection Logic should return
      a ``java.lang.Boolean`` value ``true`` if the logic executed
      correctly. If the logic fails for some reason then ``false`` can
      be returned, but this will cause the policy invoking this task
      will fail and exit.

   .. note:: 
      How to return a value from Task Selection Logic
	  Some languages explicitly support returning values from the script (e.g. MVEL and 
	  JRuby) using an explicit return statement (e.g. ``return true``), other languages do not (e.g.
	  JavaScript and Jython). For languages that do not support the ``return`` statement, a special field called 
	  ``returnValue`` must be created to hold the result of the task logic operation (i.e. assign a ``java.lang.Boolean``
	  value to the ``returnValue`` field before completing the task). 
	  Also, in MVEL if there is not explicit return statement then the return value of the last executed statement will
	  return (e.g. the statement a=(1+2) will return the value 3).   

   .. container:: paragraph

      Each of the scripting languages used in Apex can import and use
      standard Java libraries to perform complex tasks. Besides imported
      classes and normal language features Apex provides some natively
      available parameters and functions that can be used directly. At
      run-time these parameters are populated by the Apex execution
      environment and made natively available to logic scripts each time
      the logic script is invoked. (These can be accessed using the
      ``executor`` keyword for most languages, or can be accessed
      directly without the ``executor`` keyword in MVEL):

   Table 2. The ``executor`` Fields / Methods
      +-------------------------------------------------------+--------------------------------------------------------+
      | Unix, Cygwin                                          | Windows                                                |
      +=======================================================+========================================================+
      | .. container::                                        | .. container::                                         |
      |                                                       |                                                        |
      |    .. container:: content                             |    .. container:: content                              |
      |                                                       |                                                        |
      |       .. code:: bash                                  |       .. code:: bash                                   |
      |         :number-lines:                                |         :number-lines:                                 |
      |                                                       |                                                        |
      |         >c:                                           |         # cd /usr/local/src/apex-pdp                   |
      |         >cd \dev\apex                                 |         # mvn clean install -DskipTest                 |
      |         >mvn clean install -DskipTests                |                                                        |
      +-------------------------------------------------------+--------------------------------------------------------+

+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| Name       | Type        | Java type                      | Description                                                                         |
+============+=============+================================+=====================================================================================+
| inFields   | Fields      | java.util.Map <String,Object>  | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    All fields in the state’s incoming event. This is implemented as a standard Java |
|            |             |                                |    Java (unmodifiable) Map                                                          |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.logger.debug("Incoming fields: "                                  |
|            |             |                                |             +executor.inFields.entrySet());                                         |
|            |             |                                |          var item_id = executor.incomingFields["item_ID"];                          |
|            |             |                                |          if (item_id >=1000) { ... }                                                |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| outFields  | Fields      | java.util.Map <String,Object>  | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    The outgoing task fields. This is implemented as a standard initially empty Java |
|            |             |                                |    (modifiable) Map. To create a new schema-compliant instance of a field object    |
|            |             |                                |    see the utility method subject.getOutFieldSchemaHelper() below                   |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.outFields["authorised"] = false;                                  |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| logger     | Logger      | org.slf4j.ext.XLogger          | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    A helpful logger                                                                 |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.logger.info("Executing task: "                                    |
|            |             |                                |             +executor.subject.id);                                                  |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| TRUE/FALSE | boolean     | java.lang.Boolean              | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    2 helpful constants. These are useful to retrieve correct return  values for the |
|            |             |                                |    task logic                                                                       |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          var returnValue = executor.isTrue;                                         |
|            |             |                                |          var returnValueType = Java.type("java.lang.Boolean");                      |
|            |             |                                |          var returnValue = new returnValueType(true);                               |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| subject    | Task        | TaskFacade                     | .. container:: paragraph                                                            |
|            |             |                                |                                                                                     |
|            |             |                                |    This provides some useful information about the task that contains this task     |
|            |             |                                |    logic. This object has some useful fields and methods :                          |
|            |             |                                |                                                                                     |
|            |             |                                | .. container:: ulist                                                                |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **AxTask task** to get access to the full task definition of                  |
|            |             |                                |       the host task                                                                 |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **String getTaskName()** to get the name of the host task                     |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **String getId()** to get the ID of the host task                             |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **SchemaHelper getInFieldSchemaHelper( String fieldName )** to                |
|            |             |                                |       get a ``SchemaHelper`` helper object to manipulate incoming                   |
|            |             |                                |       task fields in a schema-aware manner                                          |
|            |             |                                |                                                                                     |
|            |             |                                |    -  **SchemaHelper getOutFieldSchemaHelper( String fieldName )** to               |
|            |             |                                |       get a ``SchemaHelper`` helper object to manipulate outgoing                   |
|            |             |                                |       task fields in a schema-aware manner, e.g. to instantiate new                 |
|            |             |                                |       schema-compliant field objects to populate the                                |
|            |             |                                |       ``executor.outFields`` outgoing fields map                                    |
|            |             |                                |                                                                                     |
|            |             |                                | .. container::                                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |    .. container:: content                                                           |
|            |             |                                |                                                                                     |
|            |             |                                |       .. container:: paragraph                                                      |
|            |             |                                |                                                                                     |
|            |             |                                |          **Example:**                                                               |
|            |             |                                |                                                                                     |
|            |             |                                |       .. code:: javascript                                                          |
|            |             |                                |                                                                                     |
|            |             |                                |          executor.logger.info("Task name: "                                         |
|            |             |                                |             +executor.subject.getTaskName());                                       |
|            |             |                                |          executor.logger.info("Task id: "                                           |
|            |             |                                |             +executor.subject.getId());                                             |
|            |             |                                |          executor.logger.info("Task inputs definitions: "                           |
|            |             |                                |             +"executor.subject.task.getInputFieldSet());                            |
|            |             |                                |          executor.logger.info("Task outputs definitions: "                          |
|            |             |                                |             +"executor.subject.task.getOutputFieldSet());                           |
|            |             |                                |          executor.outFields["authorised"] = executor.subject                        |
|            |             |                                |                .getOutFieldSchemaHelper("authorised")                               |
|            |             |                                |               .createNewInstance("false");                                          |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+
| ContextAlbum getContextAlbum(String ctxtAlbumName )       | .. container:: paragraph                                                            |
|                                                           |                                                                                     |
|                                                           |    A utility method to retrieve a ``ContextAlbum`` for use in the task.             |
|                                                           |    This is how you access the context used by the task. The returned                |
|                                                           |    ``ContextAlbum`` implements the ``java.util.Map <String,Object>``                |
|                                                           |    interface to get and set context as appropriate. The returned                    |
|                                                           |    ``ContextAlbum`` also has methods to lock context albums, get                    |
|                                                           |    information about the schema of the items to be stored in a context              |
|                                                           |    album, and get a ``SchemaHelper`` to manipulate context album items. How         |
|                                                           |    to define and use context in a task is described in the Apex                     |
|                                                           |    Programmer’s Guide and in the My First Apex Policy guide.                        |
|                                                           |                                                                                     |
|                                                           | .. container::                                                                      |
|                                                           |                                                                                     |
|                                                           |    .. container:: content                                                           |
|                                                           |                                                                                     |
|                                                           |       .. container:: paragraph                                                      |
|                                                           |                                                                                     |
|                                                           |          **Example:**                                                               |
|                                                           |                                                                                     |
|                                                           |       .. code:: javascript                                                          |
|                                                           |                                                                                     |
|                                                           |          var bkey = executor.inFields.get("branch_ID");                             |
|                                                           |          var cnts = executor.getContextMap("BranchCounts");                         |
|                                                           |          cnts.lockForWriting(bkey);                                                 |
|                                                           |          cnts.put(bkey, cnts.get(bkey) + 1);                                        |
|                                                           |          cnts.unlockForWriting(bkey);                                               |
+------------+-------------+--------------------------------+-------------------------------------------------------------------------------------+

Logic Cheatsheet
----------------

   .. container:: paragraph

      Examples given here use Javascript (if not stated otherwise),
      other execution environments will be similar.

Add Nashorn
###########

      .. container:: paragraph

         First line in the logic use this import.

      .. container:: listingblock

         .. container:: title

            JS Nashorn

         .. container:: content

            .. code:: javascript

               load("nashorn:mozilla_compat.js");

Finish Logic with Success or Error
##################################

      .. container:: paragraph

         To finish logic, i.e. return to APEX, with success use the
         following lines close to the end of the logic.

      .. container:: listingblock

         .. container:: title

            JS Success

         .. container:: content

            .. code:: javascript

               var returnValueType = Java.type("java.lang.Boolean");
               var returnValue = new returnValueType(true);

      .. container:: paragraph

         To notify a problem, finish with an error.

      .. container:: listingblock

         .. container:: title

            JS Fail

         .. container:: content

            .. code:: javascript

               var returnValueType = Java.type("java.lang.Boolean");
               var returnValue = new returnValueType(false);

Logic Logging
#############

      .. container:: paragraph

         Logging can be made easy using a local variable for the logger.
         Line 1 below does that. Then we start with a trace log with the
         task (or task logic) identifier followed by the infields.

      .. container:: listingblock

         .. container:: title

            JS Logging

         .. container:: content

            .. code:: javascript

               var logger = executor.logger;
               logger.trace("start: " + executor.subject.id);
               logger.trace("-- infields: " + executor.inFields);

      .. container:: paragraph

         For larger logging blocks you can use the standard logging API
         to detect log levels, for instance:

      .. container:: listingblock

         .. container:: title

            JS Logging Blocks

         .. container:: content

            .. code:: javascript

               if(logger.isTraceEnabled()){
                   // trace logging block here
               }

      .. container:: paragraph

         Note: the shown logger here logs to
         ``org.onap.policy.apex.executionlogging``. The behavior of the
         actual logging can be specified in the
         ``$APEX_HOME/etc/logback.xml``.

      .. container:: paragraph

         If you want to log into the APEX root logger (which is
         sometimes necessary to report serious logic errors to the top),
         then import the required class and use this logger.

      .. container:: listingblock

         .. container:: title

            JS Root Logger

         .. container:: content

            .. code:: javascript

               importClass(org.slf4j.LoggerFactory);
               var rootLogger = LoggerFactory.getLogger(logger.ROOT_LOGGER_NAME);

               rootLogger.error("Serious error in logic detected: " + executor.subject.id);

Local Variable for Infields
###########################

      .. container:: paragraph

         It is a good idea to use local variables for ``infields``. This
         avoids long code lines and policy evolution. The following
         example assumes infields named ``nodeName`` and ``nodeAlias``.

      .. container:: listingblock

         .. container:: title

            JS Infields Local Var

         .. container:: content

            .. code:: javascript

               var ifNodeName = executor.inFields["nodeName"];
               var ifNodeAlias = executor.inFields["nodeAlias"];

Local Variable for Context Albums
#################################

      .. container:: paragraph

         Similar to the ``infields`` it is good practice to use local
         variables for context albums as well. The following example
         assumes that a task can access a context album
         ``albumTopoNodes``. The second line gets a particular node from
         this context album.

      .. container:: listingblock

         .. container:: title

            JS Infields Local Var

         .. container:: content

            .. code:: javascript

               var albumTopoNodes = executor.getContextAlbum("albumTopoNodes");
               var ctxtNode = albumTopoNodes.get(ifNodeName);

Set Outfields in Logic
######################

      .. container:: paragraph

         The task logic needs to set outfields with content generated.
         The exception are outfields that are a direct copy from an
         infield of the same name, APEX does that autmatically.

      .. container:: listingblock

         .. container:: title

            JS Set Outfields

         .. container:: content

            .. code:: javascript

               executor.outFields["report"] = "node ctxt :: added node " + ifNodeName;

Create a instance of an Outfield using Schemas
##############################################

      .. container:: paragraph

         If an outfield is not an atomic type (string, integer, etc.)
         but uses a complex schema (with a Java or Avro backend), APEX
         can help to create new instances. The ``executor`` provides a
         field called ``subject``, which provides a schem helper with an
         API for this. The complete API of the schema helper is
         documented here: `API Doc:
         SchemaHelper <https://ericsson.github.io/apex-docs/javadocs/index.html>`__.

      .. container:: paragraph

         If the backend is Avro, then an import of the Avro schema
         library is required:

      .. container:: listingblock

         .. container:: title

            JS Import Avro

         .. container:: content

            .. code:: javascript

               importClass(org.apache.avro.generic.GenericData.Array);
               importClass(org.apache.avro.generic.GenericRecord);
               importClass(org.apache.avro.Schema);

      .. container:: paragraph

         If the backend is Java, then the Java class implementing the
         schema needs to be imported.

      .. container:: paragraph

         The following example assumes an outfield ``situation``. The
         ``subject`` method ``getOutFieldSchemaHelper()`` is used to
         create a new instance.

      .. container:: listingblock

         .. container:: title

            JS Outfield Instance with Schema

         .. container:: content

            .. code:: javascript

               var situation = executor.subject.getOutFieldSchemaHelper("situation").createNewInstance();

      .. container:: paragraph

         If the schema backend is Java, the new instance will be as
         implemented in the Java class. If the schema backend is Avro,
         the new instance will have all fields from the Avro schema
         specification, but set to ``null``. So any entry here needs to
         be done separately. For instance, the ``situation`` schema has
         a field ``problemID`` which we set.

      .. container:: listingblock

         .. container:: title

            JS Outfield Instance with Schema, set

         .. container:: content

            .. code:: javascript

               situation.put("problemID", "my-problem");

Create a instance of an Context Album entry using Schemas
#########################################################

      .. container:: paragraph

         Context album instances can be created using very similar to
         the outfields. Here, the schema helper comes from the context
         album directly. The API of the schema helper is the same as for
         outfields, see `API Doc:
         SchemaHelper <https://ericsson.github.io/apex-docs/javadocs/index.html>`__.

      .. container:: paragraph

         If the backend is Avro, then an import of the Avro schema
         library is required:

      .. container:: listingblock

         .. container:: title

            JS Import Avro

         .. container:: content

            .. code:: javascript

               importClass(org.apache.avro.generic.GenericData.Array);
               importClass(org.apache.avro.generic.GenericRecord);
               importClass(org.apache.avro.Schema);

      .. container:: paragraph

         If the backend is Java, then the Java class implementing the
         schema needs to be imported.

      .. container:: paragraph

         The following example creates a new instance of a context album
         instance named ``albumProblemMap``.

      .. container:: listingblock

         .. container:: title

            JS Outfield Instance with Schema

         .. container:: content

            .. code:: javascript 

               var albumProblemMap = executor.getContextAlbum("albumProblemMap");
               var linkProblem = albumProblemMap.getSchemaHelper().createNewInstance();

      .. container:: paragraph

         This can of course be also done in a single call without the
         local variable for the context album.

      .. container:: listingblock

         .. container:: title

            JS Outfield Instance with Schema, one line

         .. container:: content

            .. code:: javascript 

               var linkProblem = executor.getContextAlbum("albumProblemMap").getSchemaHelper().createNewInstance();

      .. container:: paragraph

         If the schema backend is Java, the new instance will be as
         implemented in the Java class. If the schema backend is Avro,
         the new instance will have all fields from the Avro schema
         specification, but set to ``null``. So any entry here needs to
         be done separately (see above in outfields for an example).

Enumerates
##########

      .. container:: paragraph

         When dealing with enumerates (Avro or Java defined), it is
         sometimes and in some execution environments necessary to
         convert them to a string. For example, assume an Avro enumerate
         schema as:

      .. container:: listingblock

         .. container:: title

            Avro Enumerate Schema

         .. container:: content

            .. code:: javascript

               {
                 "type": "enum",
                 "name": "Status",
                 "symbols" : [
                   "UP",
                   "DOWN"
                 ]
               }

      .. container:: paragraph

         Using a switch over a field initialized with this enumerate in
         Javascript will fail. Instead, use the ``toString`` method, for
         example:

      .. container:: listingblock

         .. container:: title

            JS Outfield Instance with Schema, one line

         .. container:: content

            .. code:: javascript

               var switchTest = executor.inFields["status"];
               switch(switchTest.toString()){
                 case "UP": ...; break;
                 case "DOWN": ...; break;
                 default: ...;
               }

MVEL Initialize Outfields First!
################################

      .. container:: paragraph

         In MVEL, we observed a problem when accessing (setting)
         outfields without a prior access to them. So in any MVEL task
         logic, before setting any outfield, simply do a get (with any
         string), to load the outfields into the MVEL cache.

      .. container:: listingblock

         .. container:: title

            MVEL Outfield Initialization

         .. container:: content

            .. code:: javascript

               outFields.get("initialize outfields");

Using Java in Scripting Logic
#############################

      .. container:: paragraph

         Since APEX executes the logic inside a JVM, most scripting
         languages provide access to all standard Java classes. Simply
         add an import for the required class and then use it as in
         actual Java.

      .. container:: paragraph

         The following example imports ``java.util.arraylist`` into a
         Javascript logic, and then creates a new list.

      .. container:: listingblock

         .. container:: title

            JS Import ArrayList

         .. container:: content

            .. code:: javascript

               importClass(java.util.ArrayList);
               var myList = new ArrayList();

Policy Examples
^^^^^^^^^^^^^^^

My First Policy
---------------

         .. container:: paragraph

            A good starting point is the ``My First Policy`` example. It
            describes a sales problem, to which policy can be applied.
            The example details the policy background, shows how to use
            the REST Editor to create a policy, and provides details for
            running the policies. The documentation can be found:

         .. container:: ulist

            -  `My-First-Policy on the APEX
               site <https://ericsson.github.io/apex-docs/modules/examples/examples-myfirstpolicy/MyFirstPolicyHowto.html>`__

            -  `Stand-alone
               HTML <https://ericsson.github.io/apex-docs/docs-apex/html/HowTo-MyFirstPolicy.html>`__

            -  `Stand-alone
               PDF <https://ericsson.github.io/apex-docs/docs-apex/pdf/HowTo-MyFirstPolicy.pdf>`__

VPN SLA
-------

         .. container:: paragraph

            The domain Policy-controlled Video Streaming (PCVS) contains
            a policy for controlling video streams with different
            strategies. It also provides details for installing an
            actual testbed with off-the-shelve software (Mininet,
            Floodlight, Kafka, Zookeeper). The policy model here
            demonstrates virtually all APEX features: local context and
            policies controlling it, task selection logic and multiple
            tasks in a single state, AVRO schemas for context, AVOR
            schemas for events (trigger and local), and a CLI editor
            specification of the policy. The documentation can be found:

         .. container:: ulist

            -  `VPN SLA Policy on the APEX
               site <https://ericsson.github.io/apex-docs/modules/examples/examples-pcvs/vpnsla/policy.html>`__

Decision Maker
--------------

         .. container:: paragraph

            The domain Decision Maker shows a very simple policy for
            decisions. Interesting here is that the it creates a Docker
            image to run the policy and that it uses the APEX REST
            applications to update the policy on the-fly. It also has
            local context to remember past decisions, and shows how to
            use that to no make the same decision twice in a row. The
            documentation can be found:

         .. container:: ulist

            -  `Decision Maker on APEX
               site <https://ericsson.github.io/apex-docs/modules/examples/examples-decisionmaker/index.html>`__

.. container::
   :name: footer

   .. container::
      :name: footer-text

      2.0.0-SNAPSHOT
      Last updated 2018-09-04 16:04:24 IST

.. |APEX Policy Matrix| image:: images/apex-intro/ApexPolicyMatrix.png
.. |APEX Policy Model for Execution| image:: images/apex-policy-model/UmlPolicyModels.png
.. |Concepts and Keys| image:: images/apex-policy-model/ConceptsKeys.png