Defining Functional Dependency for XML

In relational model, functional dependency is a very well established concept. It is the technique used to enforce data integrity by specifying the constraints that may exist in the relations and in discovering redundancies during database design. XML as a new technology in data management need a similar technique to achieve data integrity in its environment. As the number of applications using native XML documents is increasing rapidly, there exist great interests in how to extend this concept in XML environment. However generalizing relational constraints to XML constraints is nontrivial because of the hierarchical and flexible structure of XML compared with flat representation of relational table. In this paper we propose a formal definition of functional dependency for XML that can specify constraints in hierarchical nested structure of XML. The advantage of this definition compared with the existing definitions is that, it’s able to specify constraints that hold not only in the entire document (globally) but also can scope within the sub-document (locally)