1. D. Brickley, R. Guha and A. Layman, W3C RDF Schemas (working draft), October 1998, http://www.w3.org/TR/WD-rdf-schema/.
2. S. Ceri, S. Comai, E. Damiani, P. Fraternali, S. Paraboschi and L. Tanca, XML-GL: a query language for XML documents, Technical Report 99.6, Dipartimento di Elettronica e Informazione, Politecnico di Milano, February 1999.
3. S. Comai, E. Damiani, R. Posenato and L. Tanca, A schema-based approach to modeling and querying WWW data, in: Proc. FQAS'98, Roskilde, Denmark, May 1998, LNAI 1495.
4. A. Cortesi, A. Dovier, E. Quintarelli and L. Tanca, Operational and abstract semantics of a query language for semi-structured information, in: Proc. Int. Workshop on Deductive Logic Programming (DDLP '98), 1998.
5. S.J. DeRose, XQuery: a unified syntax for linking and querying general XML documents, in: Query Languages 98.