On Defining Functional Dependency for XML

Functional dependency (FD) is one of the integrity constraints for any data model. In relational data model, FDs are well studied and are widely used in normalization theory and in key algorithm. In recent years, XML has emerged as an widely used data representation and storage format over the world wide web. The growing use of XML has necessitated the XML document semantically stronger. XML functional dependency can be one of the ways to make the XML data semantically richer. In this paper, we propose XML functional dependency (XFD), specially for the purpose of XML data transformation for semantic integration of schemas with integrity constraints. While proposing, we show how XFD is defined on the XML Document Type Definition (DTD) and is satisfied by the XML documents. We introduce the novel concept 'tuple' that produces the semantically correct tuples in the XML document during XFD satisfaction. We show that XML key is a special case of XFD. We also discuss the advantages of our proposal over other previous XFD definitions.