Xml Integrity Constraints

For its simplicity, xml is fast emerging as the dominant standard for representing data in the World Wide Web. Xml documents can easily integrate data from different sources, but they only support limited semantic specification. Starting from the traditional DTD and xml schema, this paper extends xml with functional dependencies, which are fundamental to semantic specification. To deal with the tree-like and semi-structured style of xml documents, the definition is given based on the path expressions. The functional dependency here can express not only the absolute integrity constraints in the whole document, but also the relative integrity constraints in part of the document, and the key for xml is just a special case of it. To solve the problem of logical implication, paper presents a sound and complete set of inference rules; this is also a basis for further study.A well designed DTD is very important for xml applications, which should avoid the occurrence of redundant information in the documents. Since the paper has extended xml with functional dependency, it can further define what redundant information is. This paper then gives the concept of normalized DTD, compares it with the BCNF in relational database, and provides an algorithm for converting DTD into a corresponding normalized one. One common way to integrate xml with traditional database is to store xml documents into database, and then rewrite the query of xml into a query of the database. Up to now, most of the studies just focus on the structure of xml documents, but pay little attention to the semantic information of them. This paper takes advantage of the "extended" semantic information to guide the storage in two ways. Firstly, the storage is carried on the normalized DTD, which will prevent the anomalies in the database operations. Secondly, the relational storage is based on the keys of xml, which will be directly imported as keys in the newly created relations. Compared with DTD, xml schema has many advantages in its power to define constraints, but limited work has been done about how to store documents in database based on xml schema. This paper does some research in this field, and the main contributions are about maintaining the constraints definition of xml schema in database.