Integrity constraints for XML

XML has become the de facto standard for representing and interchanging data in web-based applications. The wide use of XML has necessitated the XML document semantically richer. The integrity constraints for XML have been widely investigated over the past few years, with a focus on keys, foreign keys, functional dependencies (XFDs), multivalued dependencies (XMVDs) and inclusion dependencies (XINDs). XML Schema has the ability to define identity constraints, but there seems to be no consensus on how to specify other constraints. In this paper, we give an overview of previous work in defining XFDs, XMVDs and XINDs. Some significant problems for defining and checking these constraints are discussed. A set of requirements for a good definition and checking algorithm are proposed.