Access Control and Synchronization in XML Documents

Whenever multiple users modify XML documents concurrently, access control and synchronization of read and update operations are required. We suggest to define access rights and locks at the level of node names that are defined in the DTD of the XML document. This allows us to normalize (a subset of) XPath expressions, used e.g. in queries, such that access control and synchronization can be performed at the level of node names too. Then we show that access control and locking at the level of node names can be solved by the same technique, i.e. the identification of corresponding node names of XPath expressions. Finally, we extend our approach to predicate filters that may be used in XPath expressions for both, access control and synchronization in order to qualify a selected subset of nodes, and present a fast predicate evaluator for these predicates.