On the consistency of XML DTDs

DTD has been widely used as the schema language for XML documents. A DTD describes the structure of a collection of similar XML documents. The consistency problem of XML DTDs concerns the question that given a DTD D, if there exists any finite XML document that conforms to D. This issue is important because one wants to know whether a DTD specification is meaningful. In this paper, we formalize the notion of the consistency of DTDs, identify a sufficient and necessary condition for a DTD to be consistent, and propose a linear algorithm, DTDCon, for the consistency checking problem.