Capturing well typed references in DTDs

Surprisingly enough, there has been few investigations for typing references of semistructured data and XML documents. This paper build on a previous proposal [7] introducing simple schemas with well-typed references and showing that such schemas, called normalized ref-schemas, are expressible as formulas of Hybrid Modal Logic. The aim of the present paper is to extend normalized ref-schemas in order to allow one for general regular expressions and provide a fully general notion of schema capturing well-typed references, called ref-schemas. The main contribution of the paper is to show that ref-schemas are still expressible in Hybrid Modal Logic which entails that tools like for instance the tableau system developed in [9] can be used in order to check for constraint satisfiability in presence of refschemas.