A Survey Study on XML Functional Dependencies

There are two major kinds of XML functional dependency (FD) definitions. The first kind of XML FD includes Tree-tuple-based XML FD (tFD) and Path-based XML FD (pFD), and the second kind of XML FD includes Extended-path-based XML FD (epFD), Sub-graph-based XML FD (gFD), and Generalized-tree-tuple-based XML FD (gtFD). The relationships and differences in semantic power between these functional dependencies are analyzed, and some results are obtained as follows: (1) tFD and pFD of the first kind of XML FD have the same expressive power of XML FD. (2) epFD, gFD, and gtFD of the second kind of XML FDs have the same expressive power of XML FD, too. (3) The second kind of XML FD can deal with set elements in XML FD and have more general expressive power than the first kind of XML FD.