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/elements/OdaDataSet.java
super.checkExtends( parent );
		if ( provider != null )
			provider.checkExtends( parent );
		else
		{
			OdaDataSet odaParent = (OdaDataSet) parent;
			if ( odaParent.extensionID != null
					&& !odaParent.extensionID.equals( extensionID ) )
				throw new ExtendsException( this, parent,
						ExtendsException.DESIGN_EXCEPTION_WRONG_EXTENSION_TYPE );
			if ( extensionID != null
					&& !extensionID.equals( odaParent.extensionID ) )
				throw new ExtendsException( this, parent,
						ExtendsException.DESIGN_EXCEPTION_WRONG_EXTENSION_TYPE );
		}
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.DesignElement#validate(org.eclipse.birt.report.model.elements.ReportDesign)
	 */
	public List validate( Module module )
	{
		List list = super.validate( module );
		list
				.addAll( ExtensionValidator.getInstance( ).validate( module,
						this ) );
		return list;
	}
}