Bug 181121 Model should provide utility method for cube to get correspond dimension key.
In model cube handle, the relation of cube data set and dimension data sets are managed by a series of dimension condition handles.We need model to add utility method so that we can easily get corresponding dimension data set column names according to given cube dimension keys.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/Structure.java
* 
	 * @param module
	 *            the module information needed for the check, and records any
	 *            errors
	 * @param prop
	 *            the property whose type is element reference
	 * @return the element reference value is always returned, which contains
	 *         the information of element resolution.
	 */
	protected ElementRefValue resolveElementReference( Module module,
			StructPropertyDefn prop )
	{
		if ( prop.getTypeCode( ) != IPropertyType.ELEMENT_REF_TYPE )
			return null;
		Object value = getIntrinsicProperty( prop.getName( ) );
		assert value == null || value instanceof ElementRefValue;
		if ( value == null || module == null )
			return (ElementRefValue) value;
		ElementRefValue ref = (ElementRefValue) value;
		if ( ref.isResolved( ) )
			return ref;
		
		
		
		
		
		
		ElementRefPropertyType refType = (ElementRefPropertyType) prop
				.getType( );
		refType.resolve( module, prop, ref );