Add comparator implementations for yang kit

Issue-ID: MODELING-680
Change-Id: Ibf49703746f4895c6ba705c4286ea849e4786386
Signed-off-by: Miranda Tsing <qingshuting1@huawei.com>

32 files changed, 2664 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
index af665ab..d0d38f1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,6 +11,7 @@ target/
 *.iws
 *.iml
 *.ipr
+.idea
 
 ### Eclipse ###
 .apt_generated
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/AbstractYangStatementComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/AbstractYangStatementComparator.java
new file mode 100644
index 0000000..5e3af0f
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/AbstractYangStatementComparator.java
@@ -0,0 +1,59 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+
+
+public abstract class AbstractYangStatementComparator<T extends YangStatement> implements YangStatementComparator<T> {
+    /**
+     * constructor.
+     */
+    public AbstractYangStatementComparator() {
+    }
+
+    /**
+     * get compatibility rules.
+     *
+     * @return rules
+     */
+    public CompatibilityRules getCompatibilityRules() {
+        return CompatibilityRules.getInstance();
+    }
+
+    /**
+     * get change information.
+     *
+     * @param left  left statement
+     * @param right right statement
+     * @return list of change information.
+     */
+    protected abstract List<CompatibilityRule.ChangeInfo> getChangeInfo(T left, T right);
+
+    /**
+     * the default compatibility result.
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo change information
+     * @return compatibility result
+     */
+    protected abstract CompatibilityInfo defaultCompatibility(T left, T right,
+                                                              CompatibilityRule.ChangeInfo changeInfo);
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/AugmentComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/AugmentComparator.java
new file mode 100644
index 0000000..44fd21b
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/AugmentComparator.java
@@ -0,0 +1,50 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.stmt.Augment;
+
+public class AugmentComparator extends SchemaNodeComparator<Augment> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    public List<YangCompareResult> compare(Augment left, Augment right) {
+        if (left != null) {
+            if (left.getEffectiveSchemaNodeChildren().size() == 0) {
+                left = null;
+            }
+        }
+        if (right != null) {
+            if (right.getEffectiveSchemaNodeChildren().size() == 0) {
+                right = null;
+            }
+        }
+        List<YangCompareResult> compareResults = new ArrayList<>();
+        if (left == null && right == null) {
+            return compareResults;
+        }
+        return compareChildren(left, right);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/BaseComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/BaseComparator.java
new file mode 100644
index 0000000..d362fdd
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/BaseComparator.java
@@ -0,0 +1,53 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.Base;
+import org.yangcentral.yangkit.model.api.stmt.Identity;
+import org.yangcentral.yangkit.model.api.stmt.Type;
+
+
+public class BaseComparator extends CommonYangStatementComparator<Base> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Base left, Base right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        Base temp = left;
+        if (temp == null) {
+            temp = right;
+        }
+        if (temp.getParentStatement() instanceof Identity) {
+            if (changeInfo == CompatibilityRule.ChangeInfo.DELETED) {
+                return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                        "delete a base for identity,it's non-backward-compatible.");
+            }
+        } else if (temp.getParentStatement() instanceof Type) {
+            if (changeInfo == CompatibilityRule.ChangeInfo.ADDED) {
+                return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                        "add a new base for identity-ref, it's non-backward-compatible.");
+            }
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ChangeType.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ChangeType.java
new file mode 100644
index 0000000..6f7f818
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ChangeType.java
@@ -0,0 +1,42 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+
+
+public enum ChangeType {
+    ADD("add"),
+    MODIFY("modify"),
+    DELETE("delete");
+    private String description;
+
+    /**
+     *
+     * @param description
+     */
+    private ChangeType(String description) {
+        this.description = description;
+    }
+
+    /**
+     *
+     * @return
+     */
+    public String getName() {
+        return this.description;
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CommonYangStatementComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CommonYangStatementComparator.java
new file mode 100644
index 0000000..8b03304
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CommonYangStatementComparator.java
@@ -0,0 +1,495 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.base.Cardinality;
+import org.yangcentral.yangkit.base.YangElement;
+import org.yangcentral.yangkit.base.YangStatementDef;
+import org.yangcentral.yangkit.model.api.stmt.IdentifierRef;
+import org.yangcentral.yangkit.model.api.stmt.Referencable;
+import org.yangcentral.yangkit.model.api.stmt.SchemaNode;
+import org.yangcentral.yangkit.model.api.stmt.YangBuiltinStatement;
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+import org.yangcentral.yangkit.model.api.stmt.YangUnknown;
+
+
+public class CommonYangStatementComparator<T extends YangStatement> extends AbstractYangStatementComparator<T> {
+    public static final int OPTION_ONLY_META = 1;
+    public static final int OPTION_ONLY_SCHEMA = 2;
+    public static final int OPTION_ALL = 3;
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(T left, T right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (left == null) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.ADDED);
+            return changeInfos;
+        }
+
+        if (right == null) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.DELETED);
+            return changeInfos;
+        }
+        if (!yangStatementIsEqual(left, right)) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.CHANGED);
+        }
+
+        int leftIndex = getIndex(left);
+        int rightIndex = getIndex(right);
+        if (leftIndex != rightIndex) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED);
+        }
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param stmt
+     * @return
+     */
+    private int getIndex(T stmt) {
+        YangStatement parentStmt = stmt.getParentStatement();
+        if (null == parentStmt) {
+            return -1;
+        }
+        int index = -1;
+        for (int i = 0; i < parentStmt.getSubElements().size(); i++) {
+            YangElement subElement = parentStmt.getSubElements().get(i);
+            if (subElement instanceof YangStatement) {
+                index++;
+                if (subElement == stmt) {
+                    return index;
+                }
+            }
+        }
+        return index;
+    }
+
+    /**
+     *
+     * @param changeInfo
+     * @return
+     */
+    protected ChangeType getChangeType(CompatibilityRule.ChangeInfo changeInfo) {
+        switch (changeInfo) {
+            case ADDED:
+            case MANDATORY_ADDED: {
+                return ChangeType.ADD;
+            }
+            case DELETED: {
+                return ChangeType.DELETE;
+            }
+            default: {
+                return ChangeType.MODIFY;
+            }
+        }
+    }
+
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(T left, T right, CompatibilityRule.ChangeInfo changeInfo) {
+        return new CompatibilityInfo(CompatibilityRule.Compatibility.BC, null);
+    }
+
+    /**
+     * get statement string representation.
+     *
+     * @param stmt statement
+     * @return string
+     */
+    public static String getStatement(YangStatement stmt) {
+        if (stmt == null) {
+            return null;
+        }
+        String statement = null;
+        if (stmt instanceof YangBuiltinStatement) {
+            statement = stmt.getYangKeyword().getLocalName();
+        } else {
+            YangUnknown unknown = (YangUnknown) stmt;
+            if (unknown.getExtension() == null) {
+                return unknown.getKeyword();
+            }
+            String moduleName = unknown.getExtension().getContext().getCurModule().getMainModule().getArgStr();
+            String extensionName = unknown.getExtension().getArgStr();
+            statement = moduleName + ":" + extensionName;
+        }
+        return statement;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    protected List<YangCompareResult> compareChildren(T left, T right) {
+        List<YangCompareResult> compareResults =
+                compareStatements(left == null ? new ArrayList<>() : left.getEffectiveSubStatements(),
+                        right == null ? new ArrayList<>() : right.getEffectiveSubStatements(), OPTION_ONLY_META);
+        return compareResults;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    public List<YangCompareResult> compare(T left, T right) {
+        List<YangCompareResult> compareResults = new ArrayList<>();
+        List<CompatibilityRule.ChangeInfo> changeInfos = getChangeInfo(left, right);
+        if (!changeInfos.isEmpty()) {
+            YangStatement effectiveStmt = left == null ? right : left;
+            String statement = getStatement(effectiveStmt);
+            String parentStmt = getStatement(effectiveStmt.getParentStatement());
+            for (CompatibilityRule.ChangeInfo changeInfo : changeInfos) {
+                if (changeInfo == CompatibilityRule.ChangeInfo.IGNORE) {
+                    continue;
+                }
+                CompatibilityRule compatibilityRule = null;
+                if (null != getCompatibilityRules()) {
+                    compatibilityRule = getCompatibilityRules().searchRule(statement, parentStmt, changeInfo);
+                }
+                if (compatibilityRule == null) {
+                    //ignore sequence change
+                    if (changeInfo != CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED) {
+                        YangStatementCompareResult statementCompareResult =
+                                new YangStatementCompareResult(getChangeType(changeInfo), left, right);
+                        statementCompareResult.setCompatibilityInfo(defaultCompatibility(left, right, changeInfo));
+                        compareResults.add(statementCompareResult);
+                    }
+
+                } else {
+                    YangStatementCompareResult statementCompareResult =
+                            new YangStatementCompareResult(getChangeType(changeInfo), left, right);
+                    statementCompareResult.setCompatibilityInfo(
+                            new CompatibilityInfo(compatibilityRule.getCompatibility(),
+                                    compatibilityRule.getDescription()));
+                    compareResults.add(statementCompareResult);
+                }
+
+            }
+        }
+
+        //sub statements
+        if (left != null && right != null) {
+            compareResults.addAll(compareChildren(left, right));
+        }
+        return compareResults;
+    }
+
+    /**
+     * calculate the similarity.
+     *
+     * @param src       source statement
+     * @param candidate candidate statement
+     * @return similarity
+     */
+    public static int calSimilarity(YangStatement src, YangStatement candidate) {
+        if (!src.getYangKeyword().equals(candidate.getYangKeyword())) {
+            return 0;
+        }
+        int similarity = 1;
+
+        if (!src.equals(candidate)) {
+            return similarity;
+        }
+        similarity++;
+        List<YangStatement> srcSubStatements = src.getEffectiveSubStatements();
+        List<YangStatement> candidateSubStatements = candidate.getEffectiveSubStatements();
+        if (srcSubStatements.size() != candidateSubStatements.size()) {
+            return similarity;
+        }
+        similarity++;
+        List<YangStatement> matched = new ArrayList<>();
+        for (YangStatement srcSubStatement : srcSubStatements) {
+            int maxSubSimilarity = 0;
+            YangStatement maxsimliaritySubStatement = null;
+            for (YangStatement candidateSubStatment : candidateSubStatements) {
+                if (contains(matched, candidateSubStatment)) {
+                    continue;
+                }
+                int subSimilarity = calSimilarity(srcSubStatement, candidateSubStatment);
+                if (subSimilarity > maxSubSimilarity) {
+                    maxSubSimilarity = subSimilarity;
+                    maxsimliaritySubStatement = candidateSubStatment;
+                }
+            }
+            similarity += maxSubSimilarity;
+            matched.add(maxsimliaritySubStatement);
+        }
+        return similarity;
+
+    }
+
+    /**
+     * whether list contains an object.
+     *
+     * @param list a list
+     * @param obj  object
+     * @return true or false
+     */
+    public static boolean contains(List list, Object obj) {
+        if (list == null) {
+            return false;
+        }
+        for (Object src : list) {
+            if (src == obj) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * search statement from target except matched statements.
+     *
+     * @param statement statement
+     * @param target    target statements
+     * @param matched   matched statements
+     * @return the searched statement
+     */
+    public static YangStatement searchStatement(YangStatement statement, List<YangStatement> target,
+                                                List<YangStatement> matched) {
+        if (null == target || target.size() == 0) {
+            return null;
+        }
+        List<YangStatement> matchedTargetStmts = new ArrayList<>();
+        for (YangStatement rightSubStatement : target) {
+            if (contains(matched, rightSubStatement)) {
+                continue;
+            }
+            if (yangStatementIsEqual(statement, rightSubStatement)) {
+                matchedTargetStmts.add(rightSubStatement);
+                continue;
+            }
+        }
+        if (matchedTargetStmts.size() == 1) {
+            return matchedTargetStmts.get(0);
+        } else if (matchedTargetStmts.size() > 1) {
+            int maxSimilarity = 0;
+            YangStatement maxSimilarStatement = null;
+            for (YangStatement matchedTargetStmt : matchedTargetStmts) {
+                int similarity = calSimilarity(statement, matchedTargetStmt);
+                if (similarity <= 1) {
+                    continue;
+                }
+                if (similarity > maxSimilarity) {
+                    maxSimilarity = similarity;
+                    maxSimilarStatement = matchedTargetStmt;
+                }
+            }
+            if (maxSimilarStatement != null) {
+                return maxSimilarStatement;
+            }
+        }
+
+        if (statement.getParentStatement() == null) {
+            return null;
+        }
+
+        YangStatementDef statementDef = statement.getContext().getYangSpecification()
+                .getStatementDef(statement.getParentStatement().getYangKeyword());
+        if (statementDef == null) {
+            if (statement.getParentStatement() instanceof YangUnknown) {
+                //unknown will be treated as cardinality with non-unbounded
+                for (YangStatement rightSubStatement : target) {
+                    if (contains(matched, rightSubStatement)) {
+                        continue;
+                    }
+                    return rightSubStatement;
+                }
+                return null;
+            } else {
+                return null;
+            }
+        }
+
+        Cardinality cardinality = statementDef.getSubStatementCardinality(statement.getYangKeyword());
+        if (cardinality == null) {
+            if (statement instanceof YangUnknown) {
+                //unknown will be treated as cardinality with non-unbounded
+                for (YangStatement rightSubStatement : target) {
+                    if (contains(matched, rightSubStatement)) {
+                        continue;
+                    }
+                    return rightSubStatement;
+                }
+            }
+            return null;
+        }
+        if (cardinality.isUnbounded()) {
+            return null;
+        }
+
+        for (YangStatement rightSubStatement : target) {
+            if (contains(matched, rightSubStatement)) {
+                continue;
+            }
+            return rightSubStatement;
+        }
+        return null;
+    }
+
+    /**
+     * whether the left statement is equal with right statement.
+     *
+     * @param left  left statement
+     * @param right right statement
+     * @return true or false
+     */
+    public static boolean yangStatementIsEqual(YangStatement left, YangStatement right) {
+        if ((left instanceof SchemaNode) && (right instanceof SchemaNode)) {
+            SchemaNode leftSchemaNode = (SchemaNode) left;
+            SchemaNode rightSchemaNode = (SchemaNode) right;
+            if (!left.getContext().getNamespace().equals(right.getContext().getNamespace())) {
+                return false;
+            }
+            if (!yangStatementIsEqual((YangStatement) leftSchemaNode.getClosestAncestorNode(),
+                    (YangStatement) rightSchemaNode.getClosestAncestorNode())) {
+                return false;
+            }
+        }
+        if ((left instanceof IdentifierRef) && (right instanceof IdentifierRef)) {
+            if (!left.getYangKeyword().equals(right.getYangKeyword())) {
+                return false;
+            }
+            YangStatement leftRefStatement = ((IdentifierRef) left).getReferenceStatement();
+            YangStatement rightRefStatement = ((IdentifierRef) right).getReferenceStatement();
+            if (leftRefStatement != null && leftRefStatement.equals(rightRefStatement)) {
+                return true;
+            } else if (leftRefStatement == null && rightRefStatement == null) {
+                if (left.getArgStr().equals(right.getArgStr())) {
+                    return true;
+                } else {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        }
+        return left.equals(right);
+    }
+
+    /**
+     * compare the two list of statements.
+     *
+     * @param leftElements  the list of left statements
+     * @param rightElements the list of right statements
+     * @param option        OPTION_ONLY_META =1/OPTION_ONLY_SCHEMA=2/OPTION_ALL=3
+     * @return compare result
+     */
+    public static List<YangCompareResult> compareStatements(List<? extends YangStatement> leftElements,
+                                                            List<? extends YangStatement> rightElements, int option) {
+        List<YangCompareResult> compareResults = new ArrayList<>();
+        List<YangStatement> foundStatements = new ArrayList<>();
+
+        if (leftElements.size() > 0) {
+            for (YangStatement subElement : leftElements) {
+                YangStatement leftSubStatement = subElement;
+                if (option == OPTION_ONLY_META) {
+                    if ((leftSubStatement instanceof SchemaNode)
+                            || (leftSubStatement instanceof Referencable)) {
+                        continue;
+                    }
+                } else if (option == OPTION_ONLY_SCHEMA) {
+                    if (!(leftSubStatement instanceof SchemaNode)) {
+                        continue;
+                    }
+                }
+                if (leftSubStatement instanceof SchemaNode) {
+                    SchemaNode leftSchemaNode = (SchemaNode) leftSubStatement;
+                    if (!leftSchemaNode.isActive()) {
+                        continue;
+                    }
+                }
+
+                List<YangStatement> rightSubStatements = new ArrayList<>();
+                for (YangStatement rightElement : rightElements) {
+                    if (leftSubStatement.getYangKeyword().equals(rightElement.getYangKeyword())) {
+                        rightSubStatements.add(rightElement);
+                    }
+                }
+                if (rightSubStatements.size() == 0) {
+                    //no right statement, so change type is delete
+                    YangStatementComparator comparator =
+                            YangComparatorRegister.getInstance().getComparator(getStatement(leftSubStatement));
+                    compareResults.addAll(comparator.compare(leftSubStatement, null));
+                    continue;
+                }
+                YangStatement matchedRightSubStatement =
+                        searchStatement(leftSubStatement, rightSubStatements, foundStatements);
+                if (null == matchedRightSubStatement) {
+                    YangStatementComparator comparator =
+                            YangComparatorRegister.getInstance().getComparator(getStatement(leftSubStatement));
+                    compareResults.addAll(comparator.compare(leftSubStatement, null));
+                } else {
+                    foundStatements.add(matchedRightSubStatement);
+                    YangStatementComparator comparator = YangComparatorRegister.getInstance().getComparator(
+                            getStatement(leftSubStatement == null ? matchedRightSubStatement : leftSubStatement));
+                    compareResults.addAll(comparator.compare(leftSubStatement, matchedRightSubStatement));
+                }
+            }
+        }
+        if (rightElements.size() > 0) {
+            for (YangStatement subElement : rightElements) {
+                if (option == OPTION_ONLY_META) {
+                    if ((subElement instanceof SchemaNode)
+                            || (subElement instanceof Referencable)) {
+                        continue;
+                    }
+                } else if (option == OPTION_ONLY_SCHEMA) {
+                    if (!(subElement instanceof SchemaNode)) {
+                        continue;
+                    }
+                }
+                if (subElement instanceof SchemaNode) {
+                    SchemaNode rightSchemaNode = (SchemaNode) subElement;
+                    if (!rightSchemaNode.isActive()) {
+                        continue;
+                    }
+                }
+                YangStatement rightSubElement = subElement;
+                if (contains(foundStatements, rightSubElement)) {
+                    continue;
+                }
+                YangStatementComparator comparator =
+                        YangComparatorRegister.getInstance().getComparator(getStatement(rightSubElement));
+                compareResults.addAll(comparator.compare(null, rightSubElement));
+            }
+        }
+        return compareResults;
+    }
+
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompareType.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompareType.java
new file mode 100644
index 0000000..acceac3
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompareType.java
@@ -0,0 +1,23 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+public enum CompareType {
+    STMT,
+    TREE,
+    COMPATIBLE_CHECK
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityInfo.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityInfo.java
new file mode 100644
index 0000000..c27993a
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityInfo.java
@@ -0,0 +1,48 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+public class CompatibilityInfo {
+    private final CompatibilityRule.Compatibility compatibility;
+    private final String description;
+
+    /**
+     * constructor.
+     * @param compatibility compatibility
+     * @param description description
+     */
+    public CompatibilityInfo(CompatibilityRule.Compatibility compatibility, String description) {
+        this.compatibility = compatibility;
+        this.description = description;
+    }
+
+    /**
+     * get the compatibility.
+     * @return compatibility.
+     */
+    public CompatibilityRule.Compatibility getCompatibility() {
+        return compatibility;
+    }
+
+    /**
+     * get the description.
+     * @return string.
+     */
+    public String getDescription() {
+        return description;
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityRule.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityRule.java
new file mode 100644
index 0000000..b983048
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityRule.java
@@ -0,0 +1,330 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.dom4j.Element;
+
+
+public class CompatibilityRule {
+    private final String ruleId;
+    private String parentStmt;
+    private final List<String> statements;//[module_name:]keyword, for example, container/huawei-extension:filter
+    //private List<RuleType> ruleTypes;//STMT OR TREE
+    private final ChangeInfo condition;
+    private List<ChangeInfo> exceptConditions;
+    private final Compatibility compatibility;
+    private String description;
+
+    /**
+     * constructor.
+     *
+     * @param ruleId        rule id
+     * @param statements    statements can be applied
+     * @param condition     matched condition
+     * @param compatibility compatibility
+     */
+    public CompatibilityRule(String ruleId, List<String> statements, ChangeInfo condition,
+                             Compatibility compatibility) {
+        this.ruleId = ruleId;
+        this.statements = statements;
+        //this.ruleTypes = ruleTypes;
+        this.condition = condition;
+        this.compatibility = compatibility;
+    }
+
+    /**
+     * get parent statement.
+     *
+     * @return statement.
+     */
+    public String getParentStmt() {
+        return parentStmt;
+    }
+
+    /**
+     * set parent statement.
+     *
+     * @param parentStmt parent statement
+     */
+    public void setParentStmt(String parentStmt) {
+        this.parentStmt = parentStmt;
+    }
+
+    /**
+     * get except conditions.
+     *
+     * @return list of change info
+     */
+    public List<ChangeInfo> getExceptConditions() {
+        return exceptConditions;
+    }
+
+    /**
+     * set except conditions.
+     *
+     * @param exceptConditions conditions
+     */
+    public void setExceptCondition(List<ChangeInfo> exceptConditions) {
+        this.exceptConditions = exceptConditions;
+    }
+
+    /**
+     * set description.
+     *
+     * @param description description.
+     */
+    public void setDescription(String description) {
+        this.description = description;
+    }
+
+    /**
+     * get rule id.
+     *
+     * @return rule id
+     */
+    public String getRuleId() {
+        return ruleId;
+    }
+
+    /**
+     * get applied statements.
+     *
+     * @return statements
+     */
+    public List<String> getStatements() {
+        return statements;
+    }
+
+
+    /**
+     * get condition.
+     *
+     * @return condition
+     */
+    public ChangeInfo getCondition() {
+        return condition;
+    }
+
+    public Compatibility getCompatibility() {
+        return compatibility;
+    }
+
+    /**
+     * get description.
+     *
+     * @return description
+     */
+    public String getDescription() {
+        return description;
+    }
+
+    /**
+     * the definition of rule type.
+     */
+    public enum RuleType {
+        STMT("stmt"),
+        TREE("tree");
+        private String name;
+
+        private RuleType(String name) {
+            this.name = name;
+        }
+
+        /**
+         * get rule type from name.
+         *
+         * @param name name
+         * @return rule type
+         */
+        public static RuleType forName(String name) {
+            if (name.equals(STMT.name)) {
+                return STMT;
+            } else if (name.equals(TREE.name)) {
+                return TREE;
+            }
+            return null;
+        }
+    }
+
+    /**
+     * the definition of change info.
+     */
+    public enum ChangeInfo {
+        ANY("any"),//any changes, including added,deleted,changed
+        IGNORE("ignore"),//ignore any changes
+        /*any sub statement is deleted for stmt type, and any schema child node is deleted for tree type
+         */
+        DELETED("deleted"),
+        /* any sub statement is added for stmt type, and any schema child node is added for tree type*/
+        ADDED("added"),
+        MANDATORY_ADDED("mandatory-added"),// add mandatory schema node
+        /*the meaning has been changed,for example, builtin-type changed for type, value changed for enumeration*/
+        CHANGED("changed"),
+        /* any sub statements sequence changed for stmt type, and any schema child nodes sequence changed for
+         tree type, it can be applied to any statement.
+         */
+        SEQUENCE_CHANGED("sequence-changed"),
+        /*expand the scope, for range,it means larger range, for length, it means larger length, for fraction-digits,
+         * it means a lower value, for min-elements, it means a lower value, for max-elements, it means a higher value,
+         * for mandatory, it means from true to false, for config, it means from false to true
+         * for unique, it means one or more attributes are deleted*/
+        EXPAND("expand"),
+        /*reduce the scope, for range,it means smaller range, for length, it means smaller length, for fraction-digits,
+         * it means a higher value, for min-elements, it means a higher value, for max-elements, it means a lower value,
+         * for mandatory, it means from false to true, for config, it means from true to false,
+         * for unique, it means new attributes are  added */
+        REDUCE("reduce"),
+        /* for example type from int8 to int16,it is treated non-backward-compatible default. it can be applied to
+        type statement*/
+        INTEGER_TYPE_CHANGED("integer-type-changed");
+        private String name;
+
+        private ChangeInfo(String name) {
+            this.name = name;
+        }
+
+        /**
+         * get name.
+         *
+         * @return name
+         */
+        public String getName() {
+            return name;
+        }
+
+        /**
+         * get change info from name.
+         *
+         * @param name name
+         * @return change info
+         */
+        public static ChangeInfo forName(String name) {
+            if (name.equals(ANY.name)) {
+                return ANY;
+            } else if (name.equals(IGNORE.getName())) {
+                return IGNORE;
+            } else if (name.equals(EXPAND.getName())) {
+                return EXPAND;
+            } else if (name.equals(REDUCE.getName())) {
+                return REDUCE;
+            } else if (name.equals(CHANGED.getName())) {
+                return CHANGED;
+            } else if (name.equals(INTEGER_TYPE_CHANGED.getName())) {
+                return INTEGER_TYPE_CHANGED;
+            } else if (name.equals(SEQUENCE_CHANGED.getName())) {
+                return SEQUENCE_CHANGED;
+            } else if (name.equals(DELETED.getName())) {
+                return DELETED;
+            } else if (name.equals(ADDED.getName())) {
+                return ADDED;
+            } else if (name.equals(MANDATORY_ADDED.getName())) {
+                return MANDATORY_ADDED;
+            }
+
+            return null;
+        }
+
+    }
+
+    /**
+     * the definition of compatibility.
+     */
+    public enum Compatibility {
+        BC("backward-compatible"),
+        NBC("non-backward-compatible"),
+        UNKNOWN("unknown");
+        private String name;
+
+        private Compatibility(String name) {
+            this.name = name;
+        }
+
+        /**
+         * get name.
+         *
+         * @return name
+         */
+        public String getName() {
+            return name;
+        }
+
+        /**
+         * get compatibility from name.
+         *
+         * @param name name
+         * @return compatibility
+         */
+        public static Compatibility forName(String name) {
+            if (name.equals(BC.getName())) {
+                return BC;
+            } else if (name.equals(NBC.name)) {
+                return NBC;
+            } else if (name.equals(UNKNOWN.name)) {
+                return UNKNOWN;
+            }
+            return null;
+        }
+    }
+
+    /**
+     * deserialize compatibility rule from xml.
+     *
+     * @param element xml element
+     * @return compatibility rule.
+     */
+    public static CompatibilityRule deserialize(Element element) {
+
+        Element statementsElement = element.element("statements");
+        List<Element> statementElementList = statementsElement.elements("statement");
+        List<String> statements = null;
+        if (statementElementList != null && statementElementList.size() > 0) {
+            statements = new ArrayList<>();
+            for (Element statementElement : statementElementList) {
+                statements.add(statementElement.getTextTrim());
+            }
+        }
+        List<RuleType> types = new ArrayList<>();
+        List<Element> typeElements = element.elements("type");
+        for (Element typeElement : typeElements) {
+            types.add(RuleType.forName(typeElement.getTextTrim()));
+        }
+        ChangeInfo condition = ChangeInfo.forName(element.elementText("condition"));
+        List<ChangeInfo> exceptConditions = null;
+        List<Element> exceptConditionElements = element.elements("except-condition");
+        if (exceptConditionElements != null && exceptConditionElements.size() > 0) {
+            exceptConditions = new ArrayList<>();
+            for (Element exceptConditionElement : exceptConditionElements) {
+                exceptConditions.add(ChangeInfo.forName(exceptConditionElement.getTextTrim()));
+            }
+        }
+        Compatibility compatibility = Compatibility.forName(element.elementText("compatible"));
+        String description = element.elementText("description");
+        Element ruleIdElement = element.element("rule-id");
+        String ruleId = ruleIdElement.getTextTrim();
+        CompatibilityRule rule = new CompatibilityRule(ruleId, statements, condition, compatibility);
+        rule.setExceptCondition(exceptConditions);
+        rule.setDescription(description);
+        Element parentStmtElement = element.element("parent-statement");
+        if (parentStmtElement != null) {
+            rule.setParentStmt(parentStmtElement.getTextTrim());
+        }
+        return rule;
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityRules.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityRules.java
new file mode 100644
index 0000000..cbab987
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/CompatibilityRules.java
@@ -0,0 +1,149 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.dom4j.Document;
+import org.dom4j.Element;
+
+public class CompatibilityRules {
+    private final List<CompatibilityRule> compatibilityRules = new ArrayList<>();
+    private static final CompatibilityRules instance = new CompatibilityRules();
+
+    private CompatibilityRules() {
+
+    }
+
+    /**
+     * add a compatibility rule.
+     *
+     * @param rule rule
+     * @return true or false
+     */
+    public boolean addCompatibilityRule(CompatibilityRule rule) {
+        if (null != getCompatibilityRule(rule.getRuleId())) {
+            return false;
+        }
+        return compatibilityRules.add(rule);
+    }
+
+    /**
+     * get compatibility rules.
+     *
+     * @return rules
+     */
+    public List<CompatibilityRule> getCompatibilityRules() {
+        return compatibilityRules;
+    }
+
+    /**
+     * get compatibility rule by specified rule id.
+     *
+     * @param ruleId rule id
+     * @return rule
+     */
+    public CompatibilityRule getCompatibilityRule(String ruleId) {
+        for (CompatibilityRule rule : compatibilityRules) {
+            if (rule.getRuleId().equals(ruleId)) {
+                return rule;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * get instance of compatibility rules.
+     *
+     * @return rules instance.
+     */
+    public static CompatibilityRules getInstance() {
+        return instance;
+    }
+
+    /**
+     * deserialize from xml document.
+     *
+     * @param document xml document
+     */
+    public void deserialize(Document document) {
+        compatibilityRules.clear();
+        Element root = document.getRootElement();
+        List<Element> children = root.elements("rule");
+        for (Element ruleElement : children) {
+            CompatibilityRule rule = CompatibilityRule.deserialize(ruleElement);
+            addCompatibilityRule(rule);
+        }
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    private boolean matchCondition(CompatibilityRule left, CompatibilityRule.ChangeInfo right) {
+        if (left.getCondition() == CompatibilityRule.ChangeInfo.ANY) {
+            return true;
+        } else if (left.getCondition() == CompatibilityRule.ChangeInfo.IGNORE) {
+            return false;
+        }
+        if (left.getCondition() == right) {
+            return true;
+        }
+        if (left.getCondition() == CompatibilityRule.ChangeInfo.CHANGED
+                && (right == CompatibilityRule.ChangeInfo.EXPAND
+                || right == CompatibilityRule.ChangeInfo.REDUCE
+                || right == CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED
+                || right == CompatibilityRule.ChangeInfo.INTEGER_TYPE_CHANGED)) {
+            if (left.getExceptConditions() != null && left.getExceptConditions().contains(right)) {
+                return false;
+            }
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * search rule by some arguments.
+     *
+     * @param statement  statement
+     * @param parentStmt parent statement
+     * @param changeInfo change info
+     * @return matched rule
+     */
+    public CompatibilityRule searchRule(String statement, String parentStmt,
+                                        CompatibilityRule.ChangeInfo changeInfo) {
+        for (CompatibilityRule rule : compatibilityRules) {
+            if (rule.getStatements().contains(statement)) {
+                if (rule.getParentStmt() != null) {
+                    if (parentStmt == null) {
+                        continue;
+                    }
+                    if (!rule.getParentStmt().equals(parentStmt)) {
+                        continue;
+                    }
+                }
+                if (matchCondition(rule, changeInfo)) {
+                    return rule;
+                }
+            }
+        }
+        return null;
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ConfigComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ConfigComparator.java
new file mode 100644
index 0000000..a0018d7
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ConfigComparator.java
@@ -0,0 +1,78 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.schema.SchemaTreeType;
+import org.yangcentral.yangkit.model.api.stmt.Config;
+import org.yangcentral.yangkit.model.api.stmt.SchemaNode;
+
+
+public class ConfigComparator extends CommonYangStatementComparator<Config> {
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(Config left, Config right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        changeInfos.addAll(super.getChangeInfo(left, right));
+        if (left.getContext().getSelf() instanceof SchemaNode) {
+            SchemaNode schemaNode = (SchemaNode) left.getContext().getSelf();
+            if (schemaNode.getSchemaTreeType() != SchemaTreeType.DATATREE) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.IGNORE);
+                return changeInfos;
+            }
+        } else if (left.getParentStatement() != null) {
+            if (left.getParentStatement() instanceof SchemaNode) {
+                SchemaNode schemaNode = (SchemaNode) left.getParentStatement();
+                if (schemaNode.getSchemaTreeType() != SchemaTreeType.DATATREE) {
+                    changeInfos.add(CompatibilityRule.ChangeInfo.IGNORE);
+                    return changeInfos;
+                }
+            }
+        }
+        if (left.isConfig() && !right.isConfig()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+        } else if (!left.isConfig() && right.isConfig()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+        }
+
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Config left, Config right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.REDUCE) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "config is changed from false to true, it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/DefaultComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/DefaultComparator.java
new file mode 100644
index 0000000..f7b1c13
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/DefaultComparator.java
@@ -0,0 +1,41 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.Default;
+
+
+public class DefaultComparator extends CommonYangStatementComparator<Default> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Default left, Default right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.DELETED
+                || changeInfo == CompatibilityRule.ChangeInfo.CHANGED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "delete or change default statement, it's non-backward-compatible");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/DescriptionComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/DescriptionComparator.java
new file mode 100644
index 0000000..2b5db1c
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/DescriptionComparator.java
@@ -0,0 +1,40 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.Description;
+
+
+public class DescriptionComparator extends CommonYangStatementComparator<Description> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Description left, Description right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.DELETED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "delete description statement, it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/EnumBitComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/EnumBitComparator.java
new file mode 100644
index 0000000..e0fb3ef
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/EnumBitComparator.java
@@ -0,0 +1,43 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+
+
+public class EnumBitComparator extends CommonYangStatementComparator {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(YangStatement left, YangStatement right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.DELETED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "delete an enum, it's non-backward-compatible.");
+        } else if (changeInfo == CompatibilityRule.ChangeInfo.ADDED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.BC,
+                    "add a new enum, it's backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/IdentifierComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/IdentifierComparator.java
new file mode 100644
index 0000000..3eff979
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/IdentifierComparator.java
@@ -0,0 +1,40 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+
+
+public class IdentifierComparator extends CommonYangStatementComparator {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(YangStatement left, YangStatement right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.DELETED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "the statement is deleted, "
+                    + "it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/IfFeatureComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/IfFeatureComparator.java
new file mode 100644
index 0000000..dfa0199
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/IfFeatureComparator.java
@@ -0,0 +1,42 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.IfFeature;
+
+
+public class IfFeatureComparator extends CommonYangStatementComparator<IfFeature> {
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(IfFeature left, IfFeature right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.ADDED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "add a new if-feature,"
+                    + "it's non-backward-compatible.");
+        } else if (changeInfo == CompatibilityRule.ChangeInfo.CHANGED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.UNKNOWN,
+                    "if-feature is changed, it's compatibility is unknown.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MandatoryComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MandatoryComparator.java
new file mode 100644
index 0000000..375d69b
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MandatoryComparator.java
@@ -0,0 +1,63 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.yangcentral.yangkit.model.api.stmt.Mandatory;
+
+
+public class MandatoryComparator extends CommonYangStatementComparator<Mandatory> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(Mandatory left, Mandatory right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+
+        if (left.getValue() && !right.getValue()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+        } else if (!left.getValue() && right.getValue()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+        }
+        if (super.getChangeInfo(left, right).contains(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED)) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED);
+        }
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Mandatory left, Mandatory right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.REDUCE) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "mandatory is changed from false to true,"
+                    + "it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MaxElementsComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MaxElementsComparator.java
new file mode 100644
index 0000000..1361ef2
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MaxElementsComparator.java
@@ -0,0 +1,69 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.stmt.MaxElements;
+
+
+public class MaxElementsComparator extends CommonYangStatementComparator<MaxElements> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(MaxElements left, MaxElements right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (left.isUnbounded() && !right.isUnbounded()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+        } else if (!left.isUnbounded() && right.isUnbounded()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+        } else if (!left.isUnbounded() && !right.isUnbounded()) {
+            if (left.getValue() < right.getValue()) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+            } else if (left.getValue() > right.getValue()) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+            }
+        }
+        if (super.getChangeInfo(left, right).contains(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED)) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED);
+        }
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(MaxElements left, MaxElements right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.REDUCE) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "the max-elements is reduced,"
+                    + "it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MinElementsComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MinElementsComparator.java
new file mode 100644
index 0000000..f97e313
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/MinElementsComparator.java
@@ -0,0 +1,63 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.stmt.MinElements;
+
+
+public class MinElementsComparator extends CommonYangStatementComparator<MinElements> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(MinElements left, MinElements right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (left.getValue() > right.getValue()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+        } else if (left.getValue() < right.getValue()) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+        }
+        if (super.getChangeInfo(left, right).contains(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED)) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED);
+        }
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(MinElements left, MinElements right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.REDUCE) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "min-elements is increased,"
+                    + "it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ModuleComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ModuleComparator.java
new file mode 100644
index 0000000..9c9bb7f
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ModuleComparator.java
@@ -0,0 +1,86 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.yangcentral.yangkit.model.api.stmt.MainModule;
+import org.yangcentral.yangkit.model.api.stmt.Module;
+
+
+
+public class ModuleComparator extends CommonYangStatementComparator<Module> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(Module left, Module right) {
+        return super.getChangeInfo(left, right);
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Module left, Module right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.DELETED
+                || changeInfo == CompatibilityRule.ChangeInfo.CHANGED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "delete a module or change module name,"
+                    + "it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<YangCompareResult> compareChildren(Module left, Module right) {
+        List<YangCompareResult> results = new ArrayList<>();
+        Module temp = left;
+        if (temp == null) {
+            temp = right;
+        }
+        results.addAll(compareStatements(left == null ? new ArrayList<>() : left.getEffectiveMetaStatements(),
+                right == null ? new ArrayList<>() : right.getEffectiveMetaStatements(), OPTION_ALL));
+        results.addAll(compareStatements(left == null ? new ArrayList<>() : left.getEffectiveLinkageStatement(),
+                right == null ? new ArrayList<>() : right.getEffectiveLinkageStatement(), OPTION_ALL));
+        if (temp instanceof MainModule) {
+            results.addAll(compareStatements(left == null ? new ArrayList<>() : left.getEffectiveDefinitionStatement(),
+                    right == null ? new ArrayList<>() : right.getEffectiveDefinitionStatement(), OPTION_ONLY_META));
+            results.addAll(compareStatements(
+                    left == null ? new ArrayList<>() : YangComparator.getEffectiveSchemaNodeChildren(left),
+                    right == null ? new ArrayList<>() : YangComparator.getEffectiveSchemaNodeChildren(right),
+                    OPTION_ONLY_SCHEMA));
+        }
+        return results;
+    }
+
+
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/NamespaceComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/NamespaceComparator.java
new file mode 100644
index 0000000..8ea9953
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/NamespaceComparator.java
@@ -0,0 +1,39 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.Namespace;
+
+
+public class NamespaceComparator extends CommonYangStatementComparator<Namespace> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Namespace left, Namespace right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.CHANGED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "namespace MUST NOT be changed.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/OperationComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/OperationComparator.java
new file mode 100644
index 0000000..58cde02
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/OperationComparator.java
@@ -0,0 +1,90 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.stmt.Operation;
+import org.yangcentral.yangkit.model.api.stmt.SchemaNode;
+import org.yangcentral.yangkit.model.api.stmt.SchemaNodeContainer;
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+
+
+
+public class OperationComparator extends SchemaNodeComparator<Operation> {
+
+    /**
+     *
+     * @param schemaNodeContainer
+     * @return
+     */
+    private boolean hasActiveSchemaChildren(SchemaNodeContainer schemaNodeContainer) {
+        for (SchemaNode schemaNode : schemaNodeContainer.getSchemaNodeChildren()) {
+            if (schemaNode.isActive()) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<YangCompareResult> compareChildren(Operation left, Operation right) {
+        List<YangCompareResult> compareResults = new ArrayList<>();
+        compareResults.addAll(compareStatements(left == null ? new ArrayList<>() : left.getEffectiveSubStatements(),
+                right == null ? new ArrayList<>() : right.getEffectiveSubStatements(), OPTION_ONLY_META));
+
+
+        List<YangStatement> leftSchemaChildren = new ArrayList<>();
+        List<YangStatement> rightSchemaChildren = new ArrayList<>();
+        //input
+        if (left.getInput() != null && left.getInput().isActive()) {
+            //check input's schema children, only more than zero can be add to left schema array
+            if (hasActiveSchemaChildren(left.getInput())) {
+                leftSchemaChildren.add(left.getInput());
+            }
+        }
+        if (right.getInput() != null && right.getInput().isActive()) {
+            //check input's schema children, only more than zero can be add to right schema array
+            if (hasActiveSchemaChildren(right.getInput())) {
+                rightSchemaChildren.add(right.getInput());
+            }
+        }
+        //output
+        if (left.getOutput() != null && left.getOutput().isActive()) {
+            //check output's schema children, only more than zero can be add to left schema array
+            if (hasActiveSchemaChildren(left.getOutput())) {
+                leftSchemaChildren.add(left.getOutput());
+            }
+        }
+        if (right.getOutput() != null && right.getOutput().isActive()) {
+            //check out's schema children, only more than zero can be add to right schema array
+            if (hasActiveSchemaChildren(right.getOutput())) {
+                rightSchemaChildren.add(right.getOutput());
+            }
+        }
+        compareResults.addAll(compareStatements(leftSchemaChildren, rightSchemaChildren, OPTION_ALL));
+        return compareResults;
+    }
+}
+
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/PatternComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/PatternComparator.java
new file mode 100644
index 0000000..83f3f9b
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/PatternComparator.java
@@ -0,0 +1,43 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.type.Pattern;
+
+
+public class PatternComparator extends CommonYangStatementComparator<Pattern> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Pattern left, Pattern right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.ADDED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "add a pattern, it's non-backward-compatible.");
+        } else if (changeInfo == CompatibilityRule.ChangeInfo.CHANGED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.UNKNOWN,
+                    "change a pattern, the compatibility is unknown.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/RangeLengthComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/RangeLengthComparator.java
new file mode 100644
index 0000000..076b7bf
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/RangeLengthComparator.java
@@ -0,0 +1,67 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.stmt.type.SectionExpression;
+
+
+public class RangeLengthComparator extends CommonYangStatementComparator<SectionExpression> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(SectionExpression left, SectionExpression right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (!left.equals(right)) {
+            if (left.isSubSet(right)) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+            } else if (right.isSubSet(left)) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+            }
+        }
+
+        List<CompatibilityRule.ChangeInfo> superChangeInfos = super.getChangeInfo(left, right);
+        if (superChangeInfos.contains(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED)) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED);
+        }
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(SectionExpression left, SectionExpression right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.REDUCE) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, "the range or length is reduced, "
+                    + "it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ReferenceComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ReferenceComparator.java
new file mode 100644
index 0000000..be50fa1
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ReferenceComparator.java
@@ -0,0 +1,40 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.Reference;
+
+
+public class ReferenceComparator extends CommonYangStatementComparator<Reference> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Reference left, Reference right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.DELETED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "delete reference, it;s non-backward-compatible");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/SchemaNodeComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/SchemaNodeComparator.java
new file mode 100644
index 0000000..ff6de53
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/SchemaNodeComparator.java
@@ -0,0 +1,182 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.stmt.SchemaNode;
+import org.yangcentral.yangkit.model.api.stmt.SchemaNodeContainer;
+
+
+
+public class SchemaNodeComparator<T extends SchemaNode> extends CommonYangStatementComparator<T> {
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(T left, T right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (left == null && right != null) {
+            if (right.isMandatory()) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.MANDATORY_ADDED);
+            } else {
+                changeInfos.add(CompatibilityRule.ChangeInfo.ADDED);
+            }
+        } else if (left != null && right == null) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.DELETED);
+        } else if (left != null && right != null) {
+            changeInfos.addAll(super.getChangeInfo(left, right));
+        }
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(T left, T right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.MANDATORY_ADDED
+                || changeInfo == CompatibilityRule.ChangeInfo.DELETED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, null);
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<YangCompareResult> compareChildren(T left, T right) {
+        List<YangCompareResult> results = new ArrayList<>();
+        results.addAll(super.compareChildren(left, right));
+
+        SchemaNode temp = left;
+        if (temp == null) {
+            temp = right;
+        }
+        if ((temp instanceof SchemaNodeContainer)) {
+            SchemaNodeContainer leftContainer = (SchemaNodeContainer) left;
+            SchemaNodeContainer rightContainer = (SchemaNodeContainer) right;
+            results.addAll(compareStatements(leftContainer == null ? new ArrayList<>() :
+                            YangComparator.getEffectiveSchemaNodeChildren(leftContainer),
+                    rightContainer == null ? new ArrayList<>() :
+                            YangComparator.getEffectiveSchemaNodeChildren(rightContainer), OPTION_ONLY_SCHEMA));
+        }
+        return results;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    public List<YangCompareResult> compare(T left, T right) {
+        List<YangCompareResult> compareResults = new ArrayList<>();
+        if (left == null && right == null) {
+            return compareResults;
+        }
+        List<CompatibilityRule.ChangeInfo> changeInfos = getChangeInfo(left, right);
+        List<YangTreeCompareResult> treeCompareResults = new ArrayList<>();
+        SchemaNode temp = right;
+        if (temp == null) {
+            temp = left;
+        }
+        String statement = getStatement(temp);
+        String parentStatement = getStatement(temp.getParentStatement());
+        if (!changeInfos.isEmpty()) {
+            for (CompatibilityRule.ChangeInfo changeInfo : changeInfos) {
+
+                CompatibilityRule compatibilityRule = null;
+                if (getCompatibilityRules() != null) {
+                    compatibilityRule = getCompatibilityRules().searchRule(statement, parentStatement, changeInfo);
+                }
+                if (compatibilityRule == null) {
+                    if (changeInfo == CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED) {
+                        continue;
+                    }
+                    YangTreeCompareResult treeCompareResult =
+                            new YangTreeCompareResult(temp.getSchemaPath(), getChangeType(changeInfo));
+                    treeCompareResult.setLeft(left);
+                    treeCompareResult.setRight(right);
+                    treeCompareResult.setCompatibilityInfo(defaultCompatibility(left, right, changeInfo));
+                    treeCompareResults.add(treeCompareResult);
+                } else {
+                    YangTreeCompareResult treeCompareResult =
+                            new YangTreeCompareResult(temp.getSchemaPath(), getChangeType(changeInfo));
+                    treeCompareResult.setLeft(left);
+                    treeCompareResult.setRight(right);
+                    treeCompareResult.setCompatibilityInfo(new CompatibilityInfo(compatibilityRule.getCompatibility(),
+                            compatibilityRule.getDescription()));
+                    treeCompareResults.add(treeCompareResult);
+                }
+            }
+            compareResults.addAll(treeCompareResults);
+        }
+
+        //sub statements
+        if (left != null && right != null) {
+            List<YangCompareResult> childrenResults = compareChildren(left, right);
+            for (YangCompareResult childResult : childrenResults) {
+                if (childResult instanceof YangStatementCompareResult) {
+                    if (treeCompareResults.isEmpty()) {
+                        YangTreeCompareResult treeCompareResult =
+                                new YangTreeCompareResult(temp.getSchemaPath(), ChangeType.MODIFY);
+                        treeCompareResult.setLeft(left);
+                        treeCompareResult.setRight(right);
+                        treeCompareResult.setCompatibilityInfo(
+                                new CompatibilityInfo(CompatibilityRule.Compatibility.BC, null));
+                        treeCompareResults.add(treeCompareResult);
+                        compareResults.add(treeCompareResult);
+                    }
+                    for (YangTreeCompareResult treeCompareResult : treeCompareResults) {
+                        treeCompareResult.addMetaCompareResult(childResult);
+                        if (childResult.getCompatibilityInfo().getCompatibility()
+                                == CompatibilityRule.Compatibility.NBC) {
+                            treeCompareResult.setCompatibilityInfo(
+                                    new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, null));
+                        } else if (childResult.getCompatibilityInfo().getCompatibility()
+                                == CompatibilityRule.Compatibility.UNKNOWN) {
+                            if (treeCompareResult.getCompatibilityInfo().getCompatibility()
+                                    == CompatibilityRule.Compatibility.BC) {
+                                treeCompareResult.setCompatibilityInfo(
+                                        new CompatibilityInfo(CompatibilityRule.Compatibility.UNKNOWN, null));
+                            }
+                        }
+                    }
+                } else {
+                    compareResults.add(childResult);
+                }
+            }
+        }
+        return compareResults;
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/StatusComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/StatusComparator.java
new file mode 100644
index 0000000..8a6df4d
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/StatusComparator.java
@@ -0,0 +1,73 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.yangcentral.yangkit.model.api.stmt.Status;
+import org.yangcentral.yangkit.model.api.stmt.StatusStmt;
+
+
+
+
+public class StatusComparator extends CommonYangStatementComparator<StatusStmt> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(StatusStmt left, StatusStmt right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (!left.equals(right)) {
+            if (left.getStatus() == Status.CURRENT) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+            } else if (left.getStatus() == Status.DEPRECATED && right.getStatus() == Status.OBSOLETE) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+            } else {
+                changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+            }
+        }
+        List<CompatibilityRule.ChangeInfo> superChangeInfos = super.getChangeInfo(left, right);
+        if (superChangeInfos.contains(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED)) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED);
+        }
+        return changeInfos;
+    }
+
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(StatusStmt left, StatusStmt right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.REDUCE) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "un-acceptable change of status,"
+                    + "changed from current to deprecated or obsolete and changed from deprecated "
+                            + "to obsolete ard acceptable.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/TypeStatementComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/TypeStatementComparator.java
new file mode 100644
index 0000000..d934cfb
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/TypeStatementComparator.java
@@ -0,0 +1,122 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.yangcentral.yangkit.model.api.restriction.YangInteger;
+import org.yangcentral.yangkit.model.api.stmt.Type;
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+
+
+
+/**
+ * comparator for type statement.
+ *
+ * @since 2022-06-10
+ */
+public class TypeStatementComparator extends CommonYangStatementComparator<Type> {
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(Type left, Type right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (left == null && right != null) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.ADDED);
+            return changeInfos;
+        } else if (left != null && right == null) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.DELETED);
+            return changeInfos;
+        } else if (left == null && right == null) {
+            return changeInfos;
+        }
+        if (left.getRestriction().getClass() == right.getRestriction().getClass()) {
+            return changeInfos;
+        }
+        if (left.getRestriction().getClass() != right.getRestriction().getClass()) {
+            if ((left.getRestriction() instanceof YangInteger) && (right.getRestriction() instanceof YangInteger)) {
+                changeInfos.add(CompatibilityRule.ChangeInfo.INTEGER_TYPE_CHANGED);
+            } else {
+                if (!changeInfos.contains(CompatibilityRule.ChangeInfo.CHANGED)) {
+                    changeInfos.add(CompatibilityRule.ChangeInfo.CHANGED);
+                }
+            }
+        }
+        return changeInfos;
+    }
+
+    @Override
+    public List<YangCompareResult> compare(Type left, Type right) {
+        List<YangCompareResult> compareResults = new ArrayList<>();
+        List<CompatibilityRule.ChangeInfo> changeInfos = getChangeInfo(left, right);
+
+        if (!changeInfos.isEmpty()) {
+            YangStatement effectiveStmt = left == null ? right : left;
+            String statement = getStatement(effectiveStmt);
+            String parentStmt = getStatement(effectiveStmt.getParentStatement());
+            for (CompatibilityRule.ChangeInfo changeInfo : changeInfos) {
+                CompatibilityRule compatibilityRule = null;
+                if (getCompatibilityRules() != null) {
+                    compatibilityRule = getCompatibilityRules().searchRule(statement, parentStmt, changeInfo);
+                }
+                if (compatibilityRule == null) {
+                    if (changeInfo == CompatibilityRule.ChangeInfo.SEQUENCE_CHANGED) {
+                        continue;
+                    }
+                    YangStatementCompareResult statementCompareResult =
+                            new YangStatementCompareResult(getChangeType(changeInfo), left, right);
+                    statementCompareResult.setCompatibilityInfo(defaultCompatibility(left, right, changeInfo));
+                    compareResults.add(statementCompareResult);
+                } else {
+                    YangStatementCompareResult statementCompareResult =
+                            new YangStatementCompareResult(getChangeType(changeInfo), left, right);
+                    statementCompareResult.setCompatibilityInfo(
+                            new CompatibilityInfo(compatibilityRule.getCompatibility(),
+                                    compatibilityRule.getDescription()));
+                    compareResults.add(statementCompareResult);
+                }
+
+            }
+        }
+
+        //sub statements
+        if (left != null && right != null) {
+            if (left.getRestriction().getClass() != right.getRestriction().getClass()) {
+                if ((left.getRestriction() instanceof YangInteger) && (right.getRestriction() instanceof YangInteger)) {
+                    compareResults.addAll(compareChildren(left, right));
+                }
+            } else {
+                compareResults.addAll(compareChildren(left, right));
+            }
+
+        }
+        return compareResults;
+    }
+
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Type left, Type right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.CHANGED
+                || changeInfo == CompatibilityRule.ChangeInfo.INTEGER_TYPE_CHANGED
+                || changeInfo == CompatibilityRule.ChangeInfo.DELETED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC, null);
+        }
+
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+
+
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/UniqueComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/UniqueComparator.java
new file mode 100644
index 0000000..1611818
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/UniqueComparator.java
@@ -0,0 +1,105 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.yangcentral.yangkit.model.api.stmt.Leaf;
+import org.yangcentral.yangkit.model.api.stmt.Unique;
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+
+
+public class UniqueComparator extends CommonYangStatementComparator<Unique> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @return
+     */
+    @Override
+    protected List<CompatibilityRule.ChangeInfo> getChangeInfo(Unique left, Unique right) {
+        List<CompatibilityRule.ChangeInfo> changeInfos = new ArrayList<>();
+        if (left == null && right != null) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.ADDED);
+        } else if (left != null && right == null) {
+            changeInfos.add(CompatibilityRule.ChangeInfo.DELETED);
+        } else {
+            if (!left.equals(right)) {
+                int leftSize = left.getUniqueNodes().size();
+                int rightSize = right.getUniqueNodes().size();
+                if (leftSize == rightSize) {
+                    changeInfos.add(CompatibilityRule.ChangeInfo.CHANGED);
+                } else if (leftSize < rightSize) {
+                    boolean notfind = false;
+                    for (int i = 0; i < leftSize; i++) {
+                        Leaf leftUnique = left.getUniqueNodes().get(i);
+                        List<YangStatement> rightUniques = new ArrayList<>();
+                        for (Leaf rightUnique : right.getUniqueNodes()) {
+                            rightUniques.add(rightUnique);
+                        }
+                        if (searchStatement(leftUnique, rightUniques, new ArrayList<>()) == null) {
+                            notfind = true;
+                        }
+                    }
+                    if (notfind) {
+                        changeInfos.add(CompatibilityRule.ChangeInfo.CHANGED);
+                    } else {
+                        changeInfos.add(CompatibilityRule.ChangeInfo.REDUCE);
+                    }
+                } else {
+                    boolean notfind = false;
+                    for (int i = 0; i < rightSize; i++) {
+                        Leaf rightUnique = right.getUniqueNodes().get(i);
+                        List<YangStatement> leftUniques = new ArrayList<>();
+                        for (Leaf leftUnique : left.getUniqueNodes()) {
+                            leftUniques.add(leftUnique);
+                        }
+                        if (searchStatement(rightUnique, leftUniques, new ArrayList<>()) == null) {
+                            notfind = true;
+                        }
+                    }
+                    if (notfind) {
+                        changeInfos.add(CompatibilityRule.ChangeInfo.CHANGED);
+                    } else {
+                        changeInfos.add(CompatibilityRule.ChangeInfo.EXPAND);
+                    }
+                }
+            }
+        }
+
+        return changeInfos;
+    }
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Unique left, Unique right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.ADDED
+                || changeInfo == CompatibilityRule.ChangeInfo.REDUCE) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "add new unique or add a new node on unique is non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/UnitsComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/UnitsComparator.java
new file mode 100644
index 0000000..f484af2
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/UnitsComparator.java
@@ -0,0 +1,41 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.Units;
+
+
+public class UnitsComparator extends CommonYangStatementComparator<Units> {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(Units left, Units right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.DELETED
+                || changeInfo == CompatibilityRule.ChangeInfo.CHANGED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "delete or change units, it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ValuePositionComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ValuePositionComparator.java
new file mode 100644
index 0000000..c680dea
--- /dev/null
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/ValuePositionComparator.java
@@ -0,0 +1,39 @@
+/*
+Copyright 2023 Huawei Technologies
+
+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.
+ */
+
+package org.onap.modeling.yangkit.comparator;
+
+import org.yangcentral.yangkit.model.api.stmt.YangStatement;
+
+
+public class ValuePositionComparator extends CommonYangStatementComparator {
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
+    @Override
+    protected CompatibilityInfo defaultCompatibility(YangStatement left, YangStatement right,
+                                                     CompatibilityRule.ChangeInfo changeInfo) {
+        if (changeInfo == CompatibilityRule.ChangeInfo.CHANGED) {
+            return new CompatibilityInfo(CompatibilityRule.Compatibility.NBC,
+                    "change value or position, it's non-backward-compatible.");
+        }
+        return super.defaultCompatibility(left, right, changeInfo);
+    }
+}
diff --git a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/WhenMustComparator.java b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/WhenMustComparator.java
index cc6992a..3825a74 100644
--- a/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/WhenMustComparator.java
+++ b/yang-comparator/src/main/java/org/onap/modeling/yangkit/comparator/WhenMustComparator.java
@@ -19,6 +19,14 @@ package org.onap.modeling.yangkit.comparator;
 import org.yangcentral.yangkit.model.api.stmt.YangStatement;
 
 public class WhenMustComparator extends CommonYangStatementComparator {
+
+    /**
+     *
+     * @param left       left statement
+     * @param right      right statement
+     * @param changeInfo
+     * @return
+     */
     @Override
     protected CompatibilityInfo defaultCompatibility(YangStatement left, YangStatement right,
                                                      CompatibilityRule.ChangeInfo changeInfo) {