XTFDs: FDs for XML Documents

Functional Dependencies (FDs) are a common constraint for many applications. Specifying FDs in XML documents, however, is difficult because XML documents do not have uniform structures. We introduce XML Template Functional Dependencies (XTFDs), which can specify FDs in XML documents, in this paper. Previously, we defined XTFDs in terms of variables only (Mok, 2005). In this paper, we extend our previous work by incorporating XPath expressions. By incorporating XPath expressions, we can express more FDs in XML documents. Since XTFDs are based on simple concepts like variables, functions, and XPath expressions, XTFDs are more intuitive than other proposals of the same purpose in the literature. We are currently comparing XTFDs with the approaches in Arenas & Libkin (2004); Vincent et al. (2004). A preliminary comparison shows that XTFDs improve the approaches in Arenas & Libkin (2004); Vincent et al. (2004) if recursive structures, mixed content and optional attributes are allowed.