diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java
index 3c4537f..1cca591 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java
@@ -37,6 +37,7 @@
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.Expression.Kind;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.base.Literal;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
@@ -1029,6 +1030,13 @@
                 : super.visit(qe, tupSource);
     }
 
+    @Override
+    public Pair<ILogicalOperator, LogicalVariable> visit(IVisitorExtension ve, Mutable<ILogicalOperator> arg)
+            throws CompilationException {
+        // Language extensions should create a child of this class.
+        throw new CompilationException(ErrorCode.COMPILATION_ILLEGAL_STATE, "Extension dispatch not implemented!");
+    }
+
     // At this point "$x in list_expr" is a quantified expression:
     // "some $y in list_expr satisfies $x = $y"
     // Look for such quantified expression with a constant list_expr ([e1, e2, ... eN])
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/AbstractExtensionClause.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/AbstractExtensionClause.java
new file mode 100644
index 0000000..af9015b
--- /dev/null
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/AbstractExtensionClause.java
@@ -0,0 +1,41 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.asterix.lang.common.base;
+
+import org.apache.asterix.common.exceptions.CompilationException;
+import org.apache.asterix.common.exceptions.ErrorCode;
+import org.apache.asterix.lang.common.visitor.base.ILangVisitor;
+
+public abstract class AbstractExtensionClause extends AbstractClause {
+    /**
+     * Parent languages should handle extension functionality via a new method in {@link IVisitorExtension}.
+     */
+    @Override
+    public <R, T> R accept(ILangVisitor<R, T> visitor, T arg) throws CompilationException {
+        throw new CompilationException(ErrorCode.COMPILATION_ILLEGAL_STATE, getSourceLocation(),
+                "Unhandled dispatch to an extension clause node!");
+    }
+
+    public abstract IVisitorExtension getVisitorExtension();
+
+    @Override
+    public final ClauseType getClauseType() {
+        return ClauseType.EXTENSION;
+    }
+}
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/Clause.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/Clause.java
index 14f836b..95ed6df 100644
--- a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/Clause.java
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/Clause.java
@@ -43,7 +43,9 @@
         SELECT_ELEMENT,
         SELECT_REGULAR,
         SELECT_SET_OPERATION,
-        UNNEST_CLAUSE
+        UNNEST_CLAUSE,
+
+        EXTENSION
     }
 
 }
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/IVisitorExtension.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/IVisitorExtension.java
new file mode 100644
index 0000000..9007eb8
--- /dev/null
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/base/IVisitorExtension.java
@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.asterix.lang.common.base;
+
+import java.util.Collection;
+
+import org.apache.asterix.common.exceptions.CompilationException;
+import org.apache.asterix.lang.common.expression.AbstractCallExpression;
+import org.apache.asterix.lang.common.expression.VariableExpr;
+import org.apache.asterix.lang.common.parser.ScopeChecker;
+import org.apache.asterix.lang.common.rewrites.VariableSubstitutionEnvironment;
+import org.apache.asterix.lang.common.visitor.base.ILangVisitor;
+import org.apache.hyracks.algebricks.common.utils.Pair;
+
+/**
+ * Contract for all extension AST nodes to allow existing rewrites to support language extensions.
+ */
+public interface IVisitorExtension {
+    Expression simpleExpressionDispatch(ILangVisitor<Expression, ILangExpression> simpleExpressionVisitor,
+            ILangExpression argument) throws CompilationException;
+
+    Void freeVariableDispatch(ILangVisitor<Void, Collection<VariableExpr>> freeVariableVisitor,
+            Collection<VariableExpr> freeVariables) throws CompilationException;
+
+    Void bindingVariableDispatch(ILangVisitor<Void, Collection<VariableExpr>> bindingVariableVisitor,
+            Collection<VariableExpr> bindingVariables) throws CompilationException;
+
+    Expression variableScopeDispatch(ILangVisitor<Expression, ILangExpression> scopingVisitor, ILangExpression argument,
+            ScopeChecker scopeChecker) throws CompilationException;
+
+    ILangExpression deepCopyDispatch(ILangVisitor<ILangExpression, Void> deepCopyVisitor) throws CompilationException;
+
+    Pair<ILangExpression, VariableSubstitutionEnvironment> remapCloneDispatch(
+            ILangVisitor<Pair<ILangExpression, VariableSubstitutionEnvironment>, VariableSubstitutionEnvironment> remapCloneVisitor,
+            VariableSubstitutionEnvironment substitutionEnvironment) throws CompilationException;
+
+    Boolean inlineUDFsDispatch(ILangVisitor<Boolean, Void> inlineUDFsVisitor) throws CompilationException;
+
+    Void gatherFunctionsDispatch(ILangVisitor<Void, Void> gatherFunctionsVisitor,
+            Collection<? super AbstractCallExpression> functionCalls) throws CompilationException;
+
+    Boolean checkSubqueryDispatch(ILangVisitor<Boolean, ILangExpression> checkSubqueryVisitor, ILangExpression argument)
+            throws CompilationException;
+
+    Boolean check92AggregateDispatch(ILangVisitor<Boolean, ILangExpression> check92AggregateVisitor,
+            ILangExpression argument) throws CompilationException;
+
+    Boolean checkNonFunctionalDispatch(ILangVisitor<Boolean, Void> checkNonFunctionalVisitor)
+            throws CompilationException;
+
+    Boolean checkDatasetOnlyDispatch(ILangVisitor<Boolean, VariableExpr> checkDatasetOnlyVisitor,
+            VariableExpr datasetCandidate) throws CompilationException;
+}
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/AbstractInlineUdfsVisitor.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/AbstractInlineUdfsVisitor.java
index 52775d3..077748d 100644
--- a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/AbstractInlineUdfsVisitor.java
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/AbstractInlineUdfsVisitor.java
@@ -31,6 +31,7 @@
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.Expression.Kind;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -264,6 +265,11 @@
     }
 
     @Override
+    public Boolean visit(IVisitorExtension ve, Void arg) throws CompilationException {
+        return ve.inlineUDFsDispatch(this);
+    }
+
+    @Override
     public Boolean visit(InsertStatement insert, Void arg) throws CompilationException {
         boolean changed = false;
         Expression returnExpression = insert.getReturnExpression();
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/CloneAndSubstituteVariablesVisitor.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/CloneAndSubstituteVariablesVisitor.java
index d73c264..06f22b7 100644
--- a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/CloneAndSubstituteVariablesVisitor.java
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/CloneAndSubstituteVariablesVisitor.java
@@ -29,6 +29,7 @@
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.Expression.Kind;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -339,6 +340,12 @@
     }
 
     @Override
+    public Pair<ILangExpression, VariableSubstitutionEnvironment> visit(IVisitorExtension ve,
+            VariableSubstitutionEnvironment arg) throws CompilationException {
+        return ve.remapCloneDispatch(this, arg);
+    }
+
+    @Override
     public Pair<ILangExpression, VariableSubstitutionEnvironment> visit(FieldAccessor fa,
             VariableSubstitutionEnvironment env) throws CompilationException {
         Pair<ILangExpression, VariableSubstitutionEnvironment> p = fa.getExpr().accept(this, env);
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/GatherFunctionCallsVisitor.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/GatherFunctionCallsVisitor.java
index b7cf7af..6dcfb83 100644
--- a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/GatherFunctionCallsVisitor.java
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/GatherFunctionCallsVisitor.java
@@ -25,6 +25,7 @@
 
 import org.apache.asterix.common.exceptions.CompilationException;
 import org.apache.asterix.lang.common.base.Expression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -227,6 +228,11 @@
     }
 
     @Override
+    public Void visit(IVisitorExtension ve, Void arg) throws CompilationException {
+        return ve.gatherFunctionsDispatch(this, calls);
+    }
+
+    @Override
     public Void visit(WhereClause wc, Void arg) throws CompilationException {
         wc.getWhereExpr().accept(this, arg);
         return null;
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/AbstractAstVisitor.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/AbstractAstVisitor.java
index a422ef1..a6092c6 100644
--- a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/AbstractAstVisitor.java
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/AbstractAstVisitor.java
@@ -19,6 +19,8 @@
 package org.apache.asterix.lang.common.visitor.base;
 
 import org.apache.asterix.common.exceptions.CompilationException;
+import org.apache.asterix.common.exceptions.ErrorCode;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -130,4 +132,8 @@
         return null;
     }
 
+    @Override
+    public R visit(IVisitorExtension ve, T arg) throws CompilationException {
+        throw new CompilationException(ErrorCode.COMPILATION_ILLEGAL_STATE, "Extension dispatch not implemented!");
+    }
 }
diff --git a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/ILangVisitor.java b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/ILangVisitor.java
index b9de347..8fda66e 100644
--- a/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/ILangVisitor.java
+++ b/asterixdb/asterix-lang-common/src/main/java/org/apache/asterix/lang/common/visitor/base/ILangVisitor.java
@@ -19,6 +19,7 @@
 package org.apache.asterix.lang.common.visitor.base;
 
 import org.apache.asterix.common.exceptions.CompilationException;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -222,4 +223,6 @@
     R visit(ViewDropStatement vds, T arg) throws CompilationException;
 
     R visit(ViewDecl vd, T arg) throws CompilationException;
+
+    R visit(IVisitorExtension ve, T arg) throws CompilationException;
 }
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppGroupByVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppGroupByVisitor.java
index d337de9..c4fb951 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppGroupByVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppGroupByVisitor.java
@@ -124,7 +124,8 @@
         return expr.accept(visitor, selectBlock);
     }
 
-    private List<Pair<Expression, Identifier>> createGroupFieldList(SelectBlock selectBlock) {
+    private List<Pair<Expression, Identifier>> createGroupFieldList(SelectBlock selectBlock)
+            throws CompilationException {
         List<Pair<Expression, Identifier>> groupFieldList = new ArrayList<>();
         addToFieldList(groupFieldList, SqlppVariableUtil.getBindingVariables(selectBlock.getFromClause()));
         addToFieldList(groupFieldList, SqlppVariableUtil.getLetBindingVariables(selectBlock.getLetWhereList()));
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppWindowAggregationSugarVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppWindowAggregationSugarVisitor.java
index bf3e227..aa548519 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppWindowAggregationSugarVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/rewrites/visitor/SqlppWindowAggregationSugarVisitor.java
@@ -139,7 +139,8 @@
         winExpr.setExprList(newExprList);
     }
 
-    private List<Pair<Expression, Identifier>> createWindowFieldList(SelectBlock selectBlock) {
+    private List<Pair<Expression, Identifier>> createWindowFieldList(SelectBlock selectBlock)
+            throws CompilationException {
         List<Pair<Expression, Identifier>> fieldList = new ArrayList<>();
         if (selectBlock != null) {
             addToFieldList(fieldList, SqlppVariableUtil.getBindingVariables(selectBlock.getFromClause()));
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/util/SqlppVariableUtil.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/util/SqlppVariableUtil.java
index 9d50160..0a8e528 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/util/SqlppVariableUtil.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/util/SqlppVariableUtil.java
@@ -29,17 +29,11 @@
 import org.apache.asterix.lang.common.base.Clause;
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.ILangExpression;
-import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
-import org.apache.asterix.lang.common.expression.GbyVariableExpressionPair;
-import org.apache.asterix.lang.common.expression.QuantifiedExpression;
 import org.apache.asterix.lang.common.expression.VariableExpr;
 import org.apache.asterix.lang.common.struct.Identifier;
-import org.apache.asterix.lang.common.struct.QuantifiedPair;
 import org.apache.asterix.lang.common.struct.VarIdentifier;
-import org.apache.asterix.lang.sqlpp.clause.AbstractBinaryCorrelateClause;
-import org.apache.asterix.lang.sqlpp.clause.FromClause;
-import org.apache.asterix.lang.sqlpp.clause.FromTerm;
+import org.apache.asterix.lang.sqlpp.visitor.BindingVariableVisitor;
 import org.apache.asterix.lang.sqlpp.visitor.FreeVariableVisitor;
 import org.apache.hyracks.algebricks.common.utils.Pair;
 import org.apache.hyracks.algebricks.core.algebra.base.ILogicalExpression;
@@ -131,61 +125,14 @@
         return freeVars;
     }
 
-    public static List<VariableExpr> getBindingVariables(FromClause fromClause) {
-        if (fromClause == null) {
+    public static List<VariableExpr> getBindingVariables(ILangExpression langExpr) throws CompilationException {
+        if (langExpr == null) {
             return Collections.emptyList();
         }
-        List<VariableExpr> bindingVars = new ArrayList<>();
-        for (FromTerm fromTerm : fromClause.getFromTerms()) {
-            bindingVars.addAll(getBindingVariables(fromTerm));
-        }
-        return bindingVars;
-    }
 
-    public static List<VariableExpr> getBindingVariables(FromTerm fromTerm) {
+        final BindingVariableVisitor visitor = new BindingVariableVisitor();
         List<VariableExpr> bindingVars = new ArrayList<>();
-        if (fromTerm == null) {
-            return bindingVars;
-        }
-        bindingVars.add(fromTerm.getLeftVariable());
-        if (fromTerm.hasPositionalVariable()) {
-            bindingVars.add(fromTerm.getPositionalVariable());
-        }
-        for (AbstractBinaryCorrelateClause correlateClause : fromTerm.getCorrelateClauses()) {
-            bindingVars.add(correlateClause.getRightVariable());
-            if (correlateClause.hasPositionalVariable()) {
-                bindingVars.add(correlateClause.getPositionalVariable());
-            }
-        }
-        return bindingVars;
-    }
-
-    public static List<VariableExpr> getBindingVariables(GroupbyClause gbyClause) {
-        List<VariableExpr> bindingVars = new ArrayList<>();
-        if (gbyClause == null) {
-            return bindingVars;
-        }
-        Set<VariableExpr> gbyKeyVars = new HashSet<>();
-        for (List<GbyVariableExpressionPair> gbyPairList : gbyClause.getGbyPairList()) {
-            for (GbyVariableExpressionPair gbyKey : gbyPairList) {
-                VariableExpr var = gbyKey.getVar();
-                if (var != null && gbyKeyVars.add(var)) {
-                    bindingVars.add(var);
-                }
-            }
-        }
-        if (gbyClause.hasDecorList()) {
-            for (GbyVariableExpressionPair gbyKey : gbyClause.getDecorPairList()) {
-                VariableExpr var = gbyKey.getVar();
-                if (var != null) {
-                    bindingVars.add(var);
-                }
-            }
-        }
-        if (gbyClause.hasWithMap()) {
-            bindingVars.addAll(gbyClause.getWithVarMap().values());
-        }
-        bindingVars.add(gbyClause.getGroupVar());
+        langExpr.accept(visitor, bindingVars);
         return bindingVars;
     }
 
@@ -203,15 +150,6 @@
         return bindingVars;
     }
 
-    public static List<VariableExpr> getBindingVariables(QuantifiedExpression qe) {
-        List<QuantifiedPair> quantifiedList = qe.getQuantifiedList();
-        List<VariableExpr> bindingVars = new ArrayList<>(quantifiedList.size());
-        for (QuantifiedPair qp : quantifiedList) {
-            bindingVars.add(qp.getVarExpr());
-        }
-        return bindingVars;
-    }
-
     public static void addToFieldVariableList(VariableExpr varExpr, List<Pair<Expression, Identifier>> outFieldList) {
         VarIdentifier var = varExpr.getVar();
         VariableExpr newVarExpr = new VariableExpr(var);
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/BindingVariableVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/BindingVariableVisitor.java
new file mode 100644
index 0000000..1b7dc24
--- /dev/null
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/BindingVariableVisitor.java
@@ -0,0 +1,101 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.asterix.lang.sqlpp.visitor;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.apache.asterix.common.exceptions.CompilationException;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
+import org.apache.asterix.lang.common.clause.GroupbyClause;
+import org.apache.asterix.lang.common.expression.GbyVariableExpressionPair;
+import org.apache.asterix.lang.common.expression.QuantifiedExpression;
+import org.apache.asterix.lang.common.expression.VariableExpr;
+import org.apache.asterix.lang.common.struct.QuantifiedPair;
+import org.apache.asterix.lang.sqlpp.clause.AbstractBinaryCorrelateClause;
+import org.apache.asterix.lang.sqlpp.clause.FromClause;
+import org.apache.asterix.lang.sqlpp.clause.FromTerm;
+import org.apache.asterix.lang.sqlpp.visitor.base.AbstractSqlppAstVisitor;
+
+public class BindingVariableVisitor extends AbstractSqlppAstVisitor<Void, Collection<VariableExpr>> {
+    @Override
+    public Void visit(FromClause fromClause, Collection<VariableExpr> bindingVars) throws CompilationException {
+        for (FromTerm fromTerm : fromClause.getFromTerms()) {
+            fromTerm.accept(this, bindingVars);
+        }
+        return null;
+    }
+
+    @Override
+    public Void visit(FromTerm fromTerm, Collection<VariableExpr> bindingVars) throws CompilationException {
+        bindingVars.add(fromTerm.getLeftVariable());
+        if (fromTerm.hasPositionalVariable()) {
+            bindingVars.add(fromTerm.getPositionalVariable());
+        }
+        for (AbstractBinaryCorrelateClause correlateClause : fromTerm.getCorrelateClauses()) {
+            bindingVars.add(correlateClause.getRightVariable());
+            if (correlateClause.hasPositionalVariable()) {
+                bindingVars.add(correlateClause.getPositionalVariable());
+            }
+        }
+        return null;
+    }
+
+    @Override
+    public Void visit(GroupbyClause groupbyClause, Collection<VariableExpr> bindingVars) throws CompilationException {
+        Set<VariableExpr> gbyKeyVars = new HashSet<>();
+        for (List<GbyVariableExpressionPair> gbyPairList : groupbyClause.getGbyPairList()) {
+            for (GbyVariableExpressionPair gbyKey : gbyPairList) {
+                VariableExpr var = gbyKey.getVar();
+                if (var != null && gbyKeyVars.add(var)) {
+                    bindingVars.add(var);
+                }
+            }
+        }
+        if (groupbyClause.hasDecorList()) {
+            for (GbyVariableExpressionPair gbyKey : groupbyClause.getDecorPairList()) {
+                VariableExpr var = gbyKey.getVar();
+                if (var != null) {
+                    bindingVars.add(var);
+                }
+            }
+        }
+        if (groupbyClause.hasWithMap()) {
+            bindingVars.addAll(groupbyClause.getWithVarMap().values());
+        }
+        bindingVars.add(groupbyClause.getGroupVar());
+        return null;
+    }
+
+    @Override
+    public Void visit(QuantifiedExpression qe, Collection<VariableExpr> bindingVars) throws CompilationException {
+        List<QuantifiedPair> quantifiedList = qe.getQuantifiedList();
+        for (QuantifiedPair qp : quantifiedList) {
+            bindingVars.add(qp.getVarExpr());
+        }
+        return null;
+    }
+
+    @Override
+    public Void visit(IVisitorExtension ve, Collection<VariableExpr> arg) throws CompilationException {
+        return ve.bindingVariableDispatch(this, arg);
+    }
+}
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckDatasetOnlyResolutionVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckDatasetOnlyResolutionVisitor.java
index e4ccef5..f700d21 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckDatasetOnlyResolutionVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckDatasetOnlyResolutionVisitor.java
@@ -21,6 +21,7 @@
 
 import org.apache.asterix.common.exceptions.CompilationException;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -160,6 +161,11 @@
     }
 
     @Override
+    public Boolean visit(IVisitorExtension ve, VariableExpr arg) throws CompilationException {
+        return ve.checkDatasetOnlyDispatch(this, arg);
+    }
+
+    @Override
     public Boolean visit(IfExpr ifexpr, VariableExpr arg) throws CompilationException {
         return false;
     }
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckNonFunctionalExpressionVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckNonFunctionalExpressionVisitor.java
index d6ee1fc..d16322e 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckNonFunctionalExpressionVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckNonFunctionalExpressionVisitor.java
@@ -22,6 +22,7 @@
 import org.apache.asterix.common.exceptions.CompilationException;
 import org.apache.asterix.common.exceptions.ErrorCode;
 import org.apache.asterix.common.functions.FunctionSignature;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.expression.CallExpr;
 import org.apache.asterix.lang.sqlpp.visitor.base.AbstractSqlppContainsExpressionVisitor;
 import org.apache.asterix.metadata.declared.MetadataProvider;
@@ -68,4 +69,9 @@
         }
         return super.visit(callExpr, arg);
     }
+
+    @Override
+    public Boolean visit(IVisitorExtension ve, Void arg) throws CompilationException {
+        return ve.checkNonFunctionalDispatch(this);
+    }
 }
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSql92AggregateVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSql92AggregateVisitor.java
index 3192541..5e6a84a 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSql92AggregateVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSql92AggregateVisitor.java
@@ -24,6 +24,7 @@
 import org.apache.asterix.common.functions.FunctionSignature;
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -157,6 +158,11 @@
     }
 
     @Override
+    public Boolean visit(IVisitorExtension ve, ILangExpression arg) throws CompilationException {
+        return ve.check92AggregateDispatch(this, arg);
+    }
+
+    @Override
     public Boolean visit(IfExpr ifexpr, ILangExpression parentSelectBlock) throws CompilationException {
         if (ifexpr.getCondExpr().accept(this, parentSelectBlock)) {
             return true;
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSubqueryVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSubqueryVisitor.java
index a903279..399e463 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSubqueryVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/CheckSubqueryVisitor.java
@@ -24,6 +24,7 @@
 
 import org.apache.asterix.common.exceptions.CompilationException;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -231,6 +232,11 @@
     }
 
     @Override
+    public Boolean visit(IVisitorExtension ve, ILangExpression arg) throws CompilationException {
+        return ve.checkSubqueryDispatch(this, arg);
+    }
+
+    @Override
     public Boolean visit(IfExpr ifexpr, ILangExpression arg) throws CompilationException {
         return visit(ifexpr.getCondExpr(), arg) || visit(ifexpr.getThenExpr(), arg) || visit(ifexpr.getElseExpr(), arg);
     }
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/DeepCopyVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/DeepCopyVisitor.java
index d74d047..07dc24e 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/DeepCopyVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/DeepCopyVisitor.java
@@ -28,6 +28,7 @@
 import org.apache.asterix.lang.common.base.AbstractClause;
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -507,6 +508,11 @@
     }
 
     @Override
+    public ILangExpression visit(IVisitorExtension ve, Void arg) throws CompilationException {
+        return ve.deepCopyDispatch(this);
+    }
+
+    @Override
     public ILangExpression visit(CaseExpression caseExpr, Void arg) throws CompilationException {
         Expression conditionExpr = (Expression) caseExpr.getConditionExpr().accept(this, arg);
         List<Expression> whenExprList = copyExprList(caseExpr.getWhenExprs(), arg);
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/FreeVariableVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/FreeVariableVisitor.java
index 9115b1c..8ab87e7 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/FreeVariableVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/FreeVariableVisitor.java
@@ -27,6 +27,7 @@
 import org.apache.asterix.lang.common.base.AbstractClause;
 import org.apache.asterix.lang.common.base.Clause.ClauseType;
 import org.apache.asterix.lang.common.base.Expression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -468,6 +469,12 @@
     }
 
     @Override
+    public Void visit(IVisitorExtension ve, Collection<VariableExpr> arg) throws CompilationException {
+        ve.freeVariableDispatch(this, arg);
+        return null;
+    }
+
+    @Override
     public Void visit(CaseExpression caseExpr, Collection<VariableExpr> freeVars) throws CompilationException {
         caseExpr.getConditionExpr().accept(this, freeVars);
         visit(caseExpr.getWhenExprs(), freeVars);
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java
index c803d83..50ebde7 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java
@@ -28,6 +28,7 @@
 import org.apache.asterix.common.metadata.DatasetFullyQualifiedName;
 import org.apache.asterix.lang.common.base.AbstractClause;
 import org.apache.asterix.lang.common.base.Expression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.base.Literal;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
@@ -373,6 +374,12 @@
     }
 
     @Override
+    public Void visit(IVisitorExtension ve, Integer arg) throws CompilationException {
+        // Language extensions should create a child of this class.
+        return null;
+    }
+
+    @Override
     public Void visit(WindowExpression winExpr, Integer step) throws CompilationException {
         out.print(skip(step) + "WINDOW ");
         printFunctionSignature(out, winExpr.getFunctionSignature(), winExpr.getFunctionSignature().getArity());
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppFormatPrintVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppFormatPrintVisitor.java
index 975379d..8052c7e 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppFormatPrintVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppFormatPrintVisitor.java
@@ -24,6 +24,7 @@
 import org.apache.asterix.common.exceptions.CompilationException;
 import org.apache.asterix.lang.common.base.AbstractClause;
 import org.apache.asterix.lang.common.base.Expression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.expression.GbyVariableExpressionPair;
@@ -284,6 +285,12 @@
     }
 
     @Override
+    public Void visit(IVisitorExtension ve, Integer arg) throws CompilationException {
+        // Language extensions should create a child of this class.
+        return null;
+    }
+
+    @Override
     public Void visit(InsertStatement insert, Integer step) throws CompilationException {
         out.print(skip(step) + "insert into " + datasetSymbol
                 + generateFullName(insert.getDataverseName(), insert.getDatasetName()) + "\n");
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppAstVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppAstVisitor.java
index e9c0e4c..7973841 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppAstVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppAstVisitor.java
@@ -19,6 +19,7 @@
 package org.apache.asterix.lang.sqlpp.visitor.base;
 
 import org.apache.asterix.common.exceptions.CompilationException;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.expression.ListSliceExpression;
 import org.apache.asterix.lang.common.visitor.base.AbstractAstVisitor;
 import org.apache.asterix.lang.sqlpp.clause.FromClause;
@@ -121,4 +122,9 @@
     public R visit(ListSliceExpression expression, T arg) throws CompilationException {
         return null;
     }
+
+    @Override
+    public R visit(IVisitorExtension ve, T arg) throws CompilationException {
+        return null;
+    }
 }
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppExpressionScopingVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppExpressionScopingVisitor.java
index 7539046..765c2be 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppExpressionScopingVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppExpressionScopingVisitor.java
@@ -32,6 +32,7 @@
 import org.apache.asterix.common.exceptions.ErrorCode;
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -413,6 +414,11 @@
         return winExpr;
     }
 
+    @Override
+    public Expression visit(IVisitorExtension ve, ILangExpression arg) throws CompilationException {
+        return ve.variableScopeDispatch(this, arg, scopeChecker);
+    }
+
     // Adds a new encountered alias identifier into a scope
     private void addNewVarSymbolToScope(Scope scope, VarIdentifier var, SourceLocation sourceLoc,
             SqlppVariableAnnotation... varAnnotations) throws CompilationException {
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppSimpleExpressionVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppSimpleExpressionVisitor.java
index ef8b43c..6bbb740 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppSimpleExpressionVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/base/AbstractSqlppSimpleExpressionVisitor.java
@@ -25,6 +25,7 @@
 import org.apache.asterix.lang.common.base.AbstractClause;
 import org.apache.asterix.lang.common.base.Expression;
 import org.apache.asterix.lang.common.base.ILangExpression;
+import org.apache.asterix.lang.common.base.IVisitorExtension;
 import org.apache.asterix.lang.common.clause.GroupbyClause;
 import org.apache.asterix.lang.common.clause.LetClause;
 import org.apache.asterix.lang.common.clause.LimitClause;
@@ -384,6 +385,11 @@
     }
 
     @Override
+    public Expression visit(IVisitorExtension ve, ILangExpression arg) throws CompilationException {
+        return ve.simpleExpressionDispatch(this, arg);
+    }
+
+    @Override
     public Expression visit(CaseExpression caseExpr, ILangExpression arg) throws CompilationException {
         caseExpr.setConditionExpr(visit(caseExpr.getConditionExpr(), arg));
         caseExpr.setWhenExprs(visit(caseExpr.getWhenExprs(), arg));
@@ -403,7 +409,7 @@
         return null;
     }
 
-    protected Expression visit(Expression expr, ILangExpression arg) throws CompilationException {
+    public Expression visit(Expression expr, ILangExpression arg) throws CompilationException {
         return postVisit(preVisit(expr).accept(this, arg));
     }