On the Complexity of Verifying Consistency of XML Specifications

XML specifications often consist of a type definition (typically, a DTD) and a set of integrity constraints. It has been shown previously that such specifications can be inconsistent, and thus it is often desirable to check consistency at compile-time. It is known [16] that for general keys and foreign keys, and DTDs, the consistency problem is undecidable; however, it becomes NP-complete when all keys are one-attribute (unary), and tractable, if no foreign keys are used. In this paper, we consider a variety of previously studied constraints for XML data, and investigate the complexity of the consistency problem. Our main conclusion is that in the presence of foreign key constraints, compile-time verification of consistency is infeasible. We look at absolute constraints that hold in the entire document, and relative constraints that only hold in a part of the document. For absolute constraints, we prove decidability and establish complexity bounds for primary multi-attribute keys and u...

• Type: Journal
• Year: 2008
• Where: SIAMCOMP
• Authors: Marcelo Arenas, Wenfei Fan, Leonid Libkin
• Keywords: Consistency Problem, Foreign Keys, Integrity Constraints, SIAMCOMP 2008