Abstract

As an essential basis of relational database theory,integrity constraints such as functional dependency providea basis for well-designed databases. Integrity constraints arealso useful for the normalization of the XML schema designin the expensive applications of XML data. As a semistructurefeature, XML data are usually located by a pathexpression and multiple data items may be represented bythe same path. Thus, functional dependencies for XMLshould be constraints between sets of XML data items if thepath expression is used. These constraints also result in dataredundancy. Same as functional dependency, this kind ofdata redundancy for XML can lead to update anomalies too.This paper proposes a kind of XML integrity constraint todescribe the dependent relationship between different sets ofXML data items, and defines a general functional dependencybased on XML node sets. Moreover, this paper proposesa group of inference rules for the implication problem ofthe XML functional dependency, and proves that they aresound and complete.