private String doc2SystemId(Element ele) {
        String documentURI = null;
        /**
         * REVISIT: Casting until DOM Level 3 interfaces are available. -- mrglavas
         */
        if(ele.getOwnerDocument() instanceof com.sun.org.apache.xerces.internal.impl.xs.opti.SchemaDOM){
            documentURI = ((com.sun.org.apache.xerces.internal.impl.xs.opti.SchemaDOM) ele.getOwnerDocument()).getDocumentURI();
        }
        return documentURI != null ? documentURI : (String) fDoc2SystemId.get(ele);
    }