摘要：As an essential basis of relational database theory, integrity constraints such as functional dependency provide a basis for well-designed databases. Integrity constraints are also useful for the normalization of the XML schema design in the expensive applications of XML data. As a semi-structure feature, XML data are usually located by a path expression and multiple data items may be represented by the same path. Thus, functional dependencies for XML should be constraints between sets of XML data items if the path expression is used. These constraints also result in data redundancy. Same as functional dependency, this kind of data redundancy for XML can lead to update anomalies too. This paper proposes a kind of XML integrity constraint to describe the dependent relationship between different sets of XML data items, and defines a general functional dependency based on XML node sets. Moreover, this paper proposes a group of inference rules for the implication problem of the XML functional dependency, and proves that they are sound and complete.
