A Lightweight XML Constraint Check and Update Framework

Support for updating XML documents has recently attracted interest. When an XML document is to conform to a given schema, the problem of structural consistency arises during updating, i.e., how to incrementally guarantee that the modified XML document continues to conform to the given XML Schema. To achieve this following the traditional database approach, the XML Schema would first have to be analyzed to construct a structured repository and the XML documents would have to be loaded into this repository before any update could be checked for possible schema constraint violation. Due to the very nature of XML being lightweight and freely shared over the Web, we instead propose a novel approach towards incremental constraint checking that follows the loosely-coupled web paradigm. Namely, we propose to rewrite an XML update query into a safe XML update query by extending the original query with appropriate constraint checking subqueries. This enhanced XML update query can then safely be executed using any existing XQuery engine that supports updates. In order to verify the feasibility of our approach, we have implemented a prototype, SAXE, that implements the above techniques by extending the Kweelt XML query engine by University of Pennsylvania with both XML update support as well as incremental constraint support.