XR-lock: locking XML data for efficient concurrency control

As the extensible Markup Language (XML) is well accepted in several different web application areas, the subsequent need for sharing XML documents by different applications and multiple users are increasing, In a multi-user environment, concurrency control of XML data becomes an important issue. Although increasing concurrency control for XML data becomes an important issue, few effective methods providing high concurrency of transactions working on the same XML document have been proposed so far. This paper proposes XR-Lock, namely, XML region lock, which can achieve high concurrency while guaranteeing the serializability of transactions to the same XML document. In the proposed method, appropriate lock operation is set to nodes contained in a region, and lock compatibility can be checked at any time to assure the concurrency. Since XR-lock are set on the low-level data accesses for XML query expression and conflicts that violate serializability are detected each time a read or a write access is requested by concurrent transactions, high performance of concurrency for XML documents can be achieved. Efficient algorithms for detecting conflicts are also proposed in this paper.