A Logical Framework for XML Reference Specification

XML emerged as the (meta) mark-up language for representing, exchanging, or storing semistructured data. The structure of an XML document may be specified through DTD (Document Type Definition) language or through the specific XML language XSchema. While the expressiveness of XML Schema allows one to specify both the structure and constraints for XML documents, DTD does not allow the specification of integrity constraints for XML documents. On the other side, DTD has a very compact notation opposed to the complex notation and syntax of XML Schema. According to this scenario, in this paper we focus on a (as much as possible) simple logic, called XHyb, expressive enough to allow the specification of the most common integrity constraints in XML documents. In particular we will deal with constraints on ID and IDREF(S) attributes, which are the common way of logically connecting parts of XML documents, besides the usual containment relation of XML elements.