diff --git a/components/apimgt/org.wso2.carbon.apimgt.impl/src/main/java/org/wso2/carbon/apimgt/impl/definitions/OASParserUtil.java b/components/apimgt/org.wso2.carbon.apimgt.impl/src/main/java/org/wso2/carbon/apimgt/impl/definitions/OASParserUtil.java
index dfbef31f08b8..ed94bf83c601 100644
--- a/components/apimgt/org.wso2.carbon.apimgt.impl/src/main/java/org/wso2/carbon/apimgt/impl/definitions/OASParserUtil.java
+++ b/components/apimgt/org.wso2.carbon.apimgt.impl/src/main/java/org/wso2/carbon/apimgt/impl/definitions/OASParserUtil.java
@@ -654,6 +654,13 @@ private static void setRefOfApiResponse(ApiResponse response, SwaggerUpdateConte
                     addToReferenceObjectMap(ref, context);
                 }
             }
+
+            Map<String, Header> headers = response.getHeaders();
+            if (headers != null) {
+                for (Header header : headers.values()) {
+                    setRefOfApiResponseHeader(header, context);
+                }
+            }
         }
     }
 
@@ -683,9 +690,14 @@ private static void setRefOfApiResponseHeader(Header header, SwaggerUpdateContex
             if (content != null) {
                 extractReferenceFromContent(content, context);
             } else {
-                String ref = header.get$ref();
-                if (ref != null) {
-                    addToReferenceObjectMap(ref, context);
+                Schema schema = header.getSchema();
+                if (schema != null) {
+                    extractReferenceFromSchema(schema, context);
+                } else {
+                    String ref = header.get$ref();
+                    if (ref != null) {
+                        addToReferenceObjectMap(ref, context);
+                    }
                 }
             }
         }
@@ -773,9 +785,15 @@ private static void extractReferenceFromSchema(Schema schema, SwaggerUpdateConte
             if (ref == null) {
                 if (schema instanceof ArraySchema) {
                     ArraySchema arraySchema = (ArraySchema) schema;
-                    ref = arraySchema.getItems().get$ref();
+                    Schema itemsSchema = arraySchema.getItems();
+                    // Process $ref items
+                    ref = itemsSchema.get$ref();
+                    if (ref == null) {
+                        // Process items in the form of Composed Schema such as allOf, oneOf, anyOf
+                        extractReferenceFromSchema(itemsSchema, context);
+                    }
                 } else if (schema instanceof ObjectSchema) {
-                    references = addSchemaOfSchema(schema);
+                    references = addSchemaOfSchema(schema, context);
                 } else if (schema instanceof MapSchema) {
                     Schema additionalPropertiesSchema = (Schema) schema.getAdditionalProperties();
                     extractReferenceFromSchema(additionalPropertiesSchema, context);
@@ -783,7 +801,7 @@ private static void extractReferenceFromSchema(Schema schema, SwaggerUpdateConte
                     if (((ComposedSchema) schema).getAllOf() != null) {
                         for (Schema sc : ((ComposedSchema) schema).getAllOf()) {
                             if (OBJECT_DATA_TYPE.equalsIgnoreCase(sc.getType())) {
-                                references.addAll(addSchemaOfSchema(sc));
+                                references.addAll(addSchemaOfSchema(sc, context));
                             } else {
                                 String schemaRef = sc.get$ref();
                                 if (schemaRef != null) {
@@ -793,10 +811,11 @@ private static void extractReferenceFromSchema(Schema schema, SwaggerUpdateConte
                                 }
                             }
                         }
-                    } else if (((ComposedSchema) schema).getAnyOf() != null) {
+                    }
+                    if (((ComposedSchema) schema).getAnyOf() != null) {
                         for (Schema sc : ((ComposedSchema) schema).getAnyOf()) {
                             if (OBJECT_DATA_TYPE.equalsIgnoreCase(sc.getType())) {
-                                references.addAll(addSchemaOfSchema(sc));
+                                references.addAll(addSchemaOfSchema(sc, context));
                             } else {
                                 String schemaRef = sc.get$ref();
                                 if (schemaRef != null) {
@@ -806,10 +825,11 @@ private static void extractReferenceFromSchema(Schema schema, SwaggerUpdateConte
                                 }
                             }
                         }
-                    } else if (((ComposedSchema) schema).getOneOf() != null) {
+                    }
+                    if (((ComposedSchema) schema).getOneOf() != null) {
                         for (Schema sc : ((ComposedSchema) schema).getOneOf()) {
                             if (OBJECT_DATA_TYPE.equalsIgnoreCase(sc.getType())) {
-                                references.addAll(addSchemaOfSchema(sc));
+                                references.addAll(addSchemaOfSchema(sc, context));
                             } else {
                                 String schemaRef = sc.get$ref();
                                 if (schemaRef != null) {
@@ -819,7 +839,10 @@ private static void extractReferenceFromSchema(Schema schema, SwaggerUpdateConte
                                 }
                             }
                         }
-                    } else {
+                    }
+                    if (((ComposedSchema) schema).getAllOf() == null &&
+                            ((ComposedSchema) schema).getAnyOf() == null &&
+                            ((ComposedSchema) schema).getOneOf() == null) {
                         log.error("Unidentified schema. The schema is not available in the API definition.");
                     }
                 }
@@ -855,13 +878,14 @@ private static void processSchemaProperties(Schema schema, SwaggerUpdateContext
         }
     }
 
-    private static List<String> addSchemaOfSchema(Schema schema) {
+    private static List<String> addSchemaOfSchema(Schema schema, SwaggerUpdateContext context) {
         List<String> references = new ArrayList<String>();
         ObjectSchema os = (ObjectSchema) schema;
         if (os.getProperties() != null) {
             for (String propertyName : os.getProperties().keySet()) {
-                if (os.getProperties().get(propertyName) instanceof ComposedSchema) {
-                    ComposedSchema cs = (ComposedSchema) os.getProperties().get(propertyName);
+                Schema propertySchema = os.getProperties().get(propertyName);
+                if (propertySchema instanceof ComposedSchema) {
+                    ComposedSchema cs = (ComposedSchema) propertySchema;
                     if (cs.getAllOf() != null) {
                         for (Schema sc : cs.getAllOf()) {
                             references.add(sc.get$ref());
@@ -877,6 +901,9 @@ private static List<String> addSchemaOfSchema(Schema schema) {
                     } else {
                         log.error("Unidentified schema. The schema is not available in the API definition.");
                     }
+                } else if (propertySchema instanceof ObjectSchema ||
+                        propertySchema instanceof ArraySchema) {
+                    extractReferenceFromSchema(propertySchema, context);
                 }
             }
         }