Path locks for XML document collaboration

The hierarchical and semistructured nature of XML data can cause complicated update-behavior. The updates are not limited to entire document trees, but can involve subtrees and even individual elements. These document parts correspond to, e.g. sections in text documents or sub-diagrams in vector graphics files. Providing suitable locking mechanisms for semi-structured data can significantly improve collaboration systems that store their data as XML documents. We show that concurrency control mechanisms in CVS, relational, and object oriented database systems are inadequate for collaboration systems based on semistructured data. We therefore propose a new locking scheme of fine granularity based on path locks. We also show that our proposed mechanism avoids conflicts by ensuring serializability, supports both top-down and bottom-up query evaluation, and is relatively efficient.