Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
if ( !extendsRef.isResolved( ) )
			resolveExtends( getRoot( ) );
		return extendsRef.getElement( );
	}
	/**
	 * Resolves the parent element reference.
	 * 
	 * @param module
	 *            the module information needed for the check
	 */
	public void resolveExtends( Module module )
	{
		if ( extendsRef == null || module == null )
			return;
		if ( extendsRef.isResolved( ) )
			return;
		
		
		
		
		
		
		ElementDefn metaData = (ElementDefn) getDefn( );
		PropertyDefn propDefn = (PropertyDefn) metaData
				.getProperty( IDesignElementModel.EXTENDS_PROP );
		int ns = metaData.getNameSpaceID( );
		DesignElement resolvedParent = module
				.resolveElement( ReferenceValueUtil.needTheNamespacePrefix(
						extendsRef, module ), ns, propDefn );
		if ( resolvedParent != null && isExtendsValid( resolvedParent ) )