diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AbstractComplexExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AbstractComplexExpectedSchemaNode.java
new file mode 100644
index 0000000..5da5149
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AbstractComplexExpectedSchemaNode.java
@@ -0,0 +1,97 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+public abstract class AbstractComplexExpectedSchemaNode extends AbstractExpectedSchemaNode {
+
+    AbstractComplexExpectedSchemaNode(AbstractComplexExpectedSchemaNode parent, SourceLocation sourceLocation,
+            String functionName) {
+        super(parent, sourceLocation, functionName);
+    }
+
+    @Override
+    public IExpectedSchemaNode replaceIfNeeded(ExpectedSchemaNodeType expectedNodeType, SourceLocation sourceLocation,
+            String functionName) {
+        //If no change is required, return the same node
+        IExpectedSchemaNode node = this;
+        if (expectedNodeType == ExpectedSchemaNodeType.ANY) {
+            /*
+             * We want to fall back to ANY. This could happen if we needed one nested value in one expression but
+             * another expression, the entire node is needed. So, we fall back to ANY and remove any information
+             * about the nested value. For example:
+             * SELECT t.hashtags[*].text, t.hashtags
+             * FROM Tweets t
+             * In this case, we first saw (t.hashtags[*].text), but the next expression (t.hashtags) requested
+             * the entire hashtags. So, the expected type for hashtags should be ANY
+             */
+            node = new AnyExpectedSchemaNode(getParent(), getSourceLocation(), getFunctionName());
+            getParent().replaceChild(this, node);
+        } else if (expectedNodeType != getType()) {
+            /*
+             * We need to change the type to UNION, as the same value was accessed as an ARRAY and as an OBJECT.
+             * This is possible if we have heterogeneous value access in the query.
+             */
+
+            //Create UNION node and its parent is the parent of this
+            UnionExpectedSchemaNode unionSchemaNode =
+                    new UnionExpectedSchemaNode(getParent(), getSourceLocation(), getFunctionName());
+
+            //Add this as a child of UNION
+            unionSchemaNode.addChild(this);
+            /*
+             * Replace the reference of this in its parent with the union node
+             * Before: parent --> this
+             * After:  parent --> UNION --> this
+             */
+            getParent().replaceChild(this, unionSchemaNode);
+            /*
+             * Set the parent of this to union
+             * Before: oldParent <-- this
+             * After:  oldParent <-- UNION <-- this
+             */
+            setParent(unionSchemaNode);
+            /*
+             * Add the new child with the expected type to union
+             * Before: UNION <-- this
+             * After:  UNION <-- (this, newChild)
+             */
+            unionSchemaNode.createChild(expectedNodeType, sourceLocation, functionName);
+            node = unionSchemaNode;
+        }
+        return node;
+    }
+
+    protected abstract void replaceChild(IExpectedSchemaNode oldNode, IExpectedSchemaNode newNode);
+
+    public static AbstractComplexExpectedSchemaNode createNestedNode(ExpectedSchemaNodeType type,
+            AbstractComplexExpectedSchemaNode parent, SourceLocation sourceLocation, String functionName) {
+        switch (type) {
+            case ARRAY:
+                return new ArrayExpectedSchemaNode(parent, sourceLocation, functionName);
+            case OBJECT:
+                return new ObjectExpectedSchemaNode(parent, sourceLocation, functionName);
+            case UNION:
+                return new UnionExpectedSchemaNode(parent, sourceLocation, functionName);
+            default:
+                throw new IllegalStateException(type + " is not nested or unknown");
+        }
+    }
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AbstractExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AbstractExpectedSchemaNode.java
new file mode 100644
index 0000000..3c6cc95
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AbstractExpectedSchemaNode.java
@@ -0,0 +1,53 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+abstract class AbstractExpectedSchemaNode implements IExpectedSchemaNode {
+    private AbstractComplexExpectedSchemaNode parent;
+    private final SourceLocation sourceLocation;
+    private final String functionName;
+
+    AbstractExpectedSchemaNode(AbstractComplexExpectedSchemaNode parent, SourceLocation sourceLocation,
+            String functionName) {
+        this.parent = parent;
+        this.sourceLocation = sourceLocation;
+        this.functionName = functionName;
+    }
+
+    @Override
+    public final AbstractComplexExpectedSchemaNode getParent() {
+        return parent;
+    }
+
+    @Override
+    public final SourceLocation getSourceLocation() {
+        return sourceLocation;
+    }
+
+    @Override
+    public final String getFunctionName() {
+        return functionName;
+    }
+
+    protected void setParent(AbstractComplexExpectedSchemaNode parent) {
+        this.parent = parent;
+    }
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AnyExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AnyExpectedSchemaNode.java
new file mode 100644
index 0000000..834a405
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/AnyExpectedSchemaNode.java
@@ -0,0 +1,58 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+public class AnyExpectedSchemaNode extends AbstractExpectedSchemaNode {
+
+    public AnyExpectedSchemaNode(AbstractComplexExpectedSchemaNode parent, SourceLocation sourceLocation,
+            String functionName) {
+        super(parent, sourceLocation, functionName);
+    }
+
+    @Override
+    public IExpectedSchemaNode replaceIfNeeded(ExpectedSchemaNodeType expectedNodeType, SourceLocation sourceLocation,
+            String functionName) {
+        if (expectedNodeType == ExpectedSchemaNodeType.ANY) {
+            return this;
+        }
+        /*
+         * ANY node is typeless (i.e., we do not know what is the possible type of ANY node) when we created it.
+         * However, now the query says it is (possibly) a nested value. We know that because there is a field
+         * access expression or an array access expression on that node. So, we should replace the ANY node to
+         * the given nested type.
+         */
+        AbstractComplexExpectedSchemaNode parent = getParent();
+        AbstractComplexExpectedSchemaNode nestedNode = AbstractComplexExpectedSchemaNode
+                .createNestedNode(expectedNodeType, parent, getSourceLocation(), functionName);
+        parent.replaceChild(this, nestedNode);
+        return nestedNode;
+    }
+
+    @Override
+    public ExpectedSchemaNodeType getType() {
+        return ExpectedSchemaNodeType.ANY;
+    }
+
+    @Override
+    public <R, T> R accept(IExpectedSchemaNodeVisitor<R, T> visitor, T arg) {
+        return visitor.visit(this, arg);
+    }
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ArrayExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ArrayExpectedSchemaNode.java
new file mode 100644
index 0000000..b000dc8
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ArrayExpectedSchemaNode.java
@@ -0,0 +1,57 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+public class ArrayExpectedSchemaNode extends AbstractComplexExpectedSchemaNode {
+    private IExpectedSchemaNode child;
+
+    ArrayExpectedSchemaNode(AbstractComplexExpectedSchemaNode parent, SourceLocation sourceLocation,
+            String functionName) {
+        super(parent, sourceLocation, functionName);
+    }
+
+    @Override
+    public ExpectedSchemaNodeType getType() {
+        return ExpectedSchemaNodeType.ARRAY;
+    }
+
+    public IExpectedSchemaNode getChild() {
+        return child;
+    }
+
+    public void addChild(IExpectedSchemaNode child) {
+        this.child = child;
+    }
+
+    @Override
+    public <R, T> R accept(IExpectedSchemaNodeVisitor<R, T> visitor, T arg) {
+        return visitor.visit(this, arg);
+    }
+
+    @Override
+    public void replaceChild(IExpectedSchemaNode oldNode, IExpectedSchemaNode newNode) {
+        if (oldNode != child) {
+            //this should not happen
+            throw new IllegalStateException("Node " + oldNode.getType() + " is not a child");
+        }
+        child = newNode;
+    }
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ExpectedSchemaNodeType.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ExpectedSchemaNodeType.java
new file mode 100644
index 0000000..e6c88b4
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ExpectedSchemaNodeType.java
@@ -0,0 +1,26 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+public enum ExpectedSchemaNodeType {
+    ARRAY,
+    OBJECT,
+    UNION,
+    ANY
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/IExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/IExpectedSchemaNode.java
new file mode 100644
index 0000000..454e32e
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/IExpectedSchemaNode.java
@@ -0,0 +1,73 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import org.apache.hyracks.algebricks.core.algebra.functions.FunctionIdentifier;
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+/**
+ * An interface of the expected schema of value access expressions in a query.
+ */
+public interface IExpectedSchemaNode {
+
+    /**
+     * @return node type
+     */
+    ExpectedSchemaNodeType getType();
+
+    /**
+     * @return source location of the value access
+     */
+    SourceLocation getSourceLocation();
+
+    /**
+     * @return value access function name
+     */
+    String getFunctionName();
+
+    /**
+     * @return the parent of a node
+     */
+    AbstractComplexExpectedSchemaNode getParent();
+
+    /**
+     * For visiting a node
+     *
+     * @param visitor schema node visitor
+     * @param arg     any argument might be needed by the visitor
+     * @param <R>     return type
+     * @param <T>     argument type
+     */
+    <R, T> R accept(IExpectedSchemaNodeVisitor<R, T> visitor, T arg);
+
+    /**
+     * Replace a node from one type to another
+     * Example:
+     * - {@link ExpectedSchemaNodeType#ANY} to {@link ExpectedSchemaNodeType#OBJECT}
+     * - {@link ExpectedSchemaNodeType#OBJECT} to {@link ExpectedSchemaNodeType#UNION}
+     *
+     * @param expectedNodeType what is the other expected type
+     * @param sourceLocation   source location of the value access
+     * @param functionName     function name as in {@link FunctionIdentifier#getName()}
+     * @see AbstractComplexExpectedSchemaNode#replaceIfNeeded(ExpectedSchemaNodeType, SourceLocation, String)
+     * @see UnionExpectedSchemaNode#replaceIfNeeded(ExpectedSchemaNodeType, SourceLocation, String)
+     */
+    IExpectedSchemaNode replaceIfNeeded(ExpectedSchemaNodeType expectedNodeType, SourceLocation sourceLocation,
+            String functionName);
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/IExpectedSchemaNodeVisitor.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/IExpectedSchemaNodeVisitor.java
new file mode 100644
index 0000000..754503a
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/IExpectedSchemaNodeVisitor.java
@@ -0,0 +1,32 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+public interface IExpectedSchemaNodeVisitor<R, T> {
+
+    R visit(RootExpectedSchemaNode node, T arg);
+
+    R visit(ObjectExpectedSchemaNode node, T arg);
+
+    R visit(ArrayExpectedSchemaNode node, T arg);
+
+    R visit(UnionExpectedSchemaNode node, T arg);
+
+    R visit(AnyExpectedSchemaNode node, T arg);
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ObjectExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ObjectExpectedSchemaNode.java
new file mode 100644
index 0000000..02307c0
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/ObjectExpectedSchemaNode.java
@@ -0,0 +1,71 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+public class ObjectExpectedSchemaNode extends AbstractComplexExpectedSchemaNode {
+    private final Map<String, IExpectedSchemaNode> children;
+
+    ObjectExpectedSchemaNode(AbstractComplexExpectedSchemaNode parent, SourceLocation sourceLocation,
+            String functionName) {
+        super(parent, sourceLocation, functionName);
+        children = new HashMap<>();
+    }
+
+    public Set<Map.Entry<String, IExpectedSchemaNode>> getChildren() {
+        return children.entrySet();
+    }
+
+    public IExpectedSchemaNode addChild(String fieldName, IExpectedSchemaNode child) {
+        children.put(fieldName, child);
+        return child;
+    }
+
+    @Override
+    public ExpectedSchemaNodeType getType() {
+        return ExpectedSchemaNodeType.OBJECT;
+    }
+
+    @Override
+    public <R, T> R accept(IExpectedSchemaNodeVisitor<R, T> visitor, T arg) {
+        return visitor.visit(this, arg);
+    }
+
+    @Override
+    public void replaceChild(IExpectedSchemaNode oldNode, IExpectedSchemaNode newNode) {
+        String key = null;
+        for (Map.Entry<String, IExpectedSchemaNode> child : children.entrySet()) {
+            if (child.getValue() == oldNode) {
+                key = child.getKey();
+                break;
+            }
+        }
+
+        if (key == null) {
+            //this should not happen
+            throw new IllegalStateException("Node " + oldNode.getType() + " is not a child");
+        }
+        children.replace(key, newNode);
+    }
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/RootExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/RootExpectedSchemaNode.java
new file mode 100644
index 0000000..1a978f3
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/RootExpectedSchemaNode.java
@@ -0,0 +1,70 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+public class RootExpectedSchemaNode extends ObjectExpectedSchemaNode {
+    //Root with zero fields
+    private static final int EMPTY_ROOT = 0;
+    //Root with the entire fields
+    private static final int ALL_FIELDS_ROOT = 1;
+    //Root with custom fields
+    private static final int CLIPPED_ROOT = 2;
+    public static final RootExpectedSchemaNode ALL_FIELDS_ROOT_NODE = new RootExpectedSchemaNode(ALL_FIELDS_ROOT);
+    public static final RootExpectedSchemaNode EMPTY_ROOT_NODE = new RootExpectedSchemaNode(EMPTY_ROOT);
+
+    private final int rootType;
+
+    RootExpectedSchemaNode() {
+        this(CLIPPED_ROOT);
+    }
+
+    private RootExpectedSchemaNode(int rootType) {
+        super(null, null, null);
+        this.rootType = rootType;
+    }
+
+    public int getRootType() {
+        return rootType;
+    }
+
+    @Override
+    public AbstractComplexExpectedSchemaNode replaceIfNeeded(ExpectedSchemaNodeType expectedNodeType,
+            SourceLocation sourceLocation, String functionName) {
+        if (rootType == ALL_FIELDS_ROOT) {
+            //ALL_FIELDS_ROOT. Return a new CLIPPED_ROOT root
+            return new RootExpectedSchemaNode();
+        }
+        return this;
+    }
+
+    @Override
+    public <R, T> R accept(IExpectedSchemaNodeVisitor<R, T> visitor, T arg) {
+        return visitor.visit(this, arg);
+    }
+
+    public boolean isEmpty() {
+        return rootType == EMPTY_ROOT;
+    }
+
+    public boolean isAllFields() {
+        return rootType == ALL_FIELDS_ROOT;
+    }
+}
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/UnionExpectedSchemaNode.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/UnionExpectedSchemaNode.java
new file mode 100644
index 0000000..3a675b8
--- /dev/null
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/pushdown/schema/UnionExpectedSchemaNode.java
@@ -0,0 +1,88 @@
+/*
+ * 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.optimizer.rules.pushdown.schema;
+
+import java.util.EnumMap;
+import java.util.Map;
+import java.util.Set;
+
+import org.apache.hyracks.api.exceptions.SourceLocation;
+
+public class UnionExpectedSchemaNode extends AbstractComplexExpectedSchemaNode {
+    private final Map<ExpectedSchemaNodeType, AbstractComplexExpectedSchemaNode> children;
+
+    protected UnionExpectedSchemaNode(AbstractComplexExpectedSchemaNode parent, SourceLocation sourceLocation,
+            String functionName) {
+        super(parent, sourceLocation, functionName);
+        children = new EnumMap<>(ExpectedSchemaNodeType.class);
+    }
+
+    /**
+     * A UNION type must have both ARRAY and OBJECT when first created - the only possible values. Thus, we cannot
+     * replace a child of a UNION type to ANY. We can only replace the union itself to ANY.
+     */
+    @Override
+    protected void replaceChild(IExpectedSchemaNode oldChildNode, IExpectedSchemaNode newChildNode) {
+        throw new UnsupportedOperationException("Cannot replace a child of UNION");
+    }
+
+    protected void addChild(AbstractComplexExpectedSchemaNode node) {
+        children.put(node.getType(), node);
+    }
+
+    public void createChild(ExpectedSchemaNodeType nodeType, SourceLocation sourceLocation, String functionName) {
+        children.computeIfAbsent(nodeType, k -> createNestedNode(k, this, sourceLocation, functionName));
+    }
+
+    public AbstractComplexExpectedSchemaNode getChild(ExpectedSchemaNodeType type) {
+        return children.get(type);
+    }
+
+    public Set<Map.Entry<ExpectedSchemaNodeType, AbstractComplexExpectedSchemaNode>> getChildren() {
+        return children.entrySet();
+    }
+
+    @Override
+    public ExpectedSchemaNodeType getType() {
+        return ExpectedSchemaNodeType.UNION;
+    }
+
+    @Override
+    public <R, T> R accept(IExpectedSchemaNodeVisitor<R, T> visitor, T arg) {
+        return visitor.visit(this, arg);
+    }
+
+    /**
+     * We override this method to handle heterogeneous values while UNION exists. We do not need to create another
+     * UNION type - we simply return this. In case we want to fallback to ANY node, we call the super method.
+     *
+     * @param expectedNodeType the expected type
+     * @param sourceLocation   source location of the value access
+     * @param functionName     function name of the expression
+     * @return ANY or this
+     */
+    @Override
+    public IExpectedSchemaNode replaceIfNeeded(ExpectedSchemaNodeType expectedNodeType, SourceLocation sourceLocation,
+            String functionName) {
+        if (expectedNodeType == ExpectedSchemaNodeType.ANY) {
+            return super.replaceIfNeeded(expectedNodeType, sourceLocation, functionName);
+        }
+        return this;
+    }
+}