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// @author Sven van der Meer (sven.van.der.meer@ericsson.com)
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== Introduction

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.

The figure shows four different views of the policy model:

* 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.

.APEX Policy Model for Execution
image::apex-policy-model/UmlPolicyModels.png[APEX Policy Model for Execution]