Xml Transaction Model And Concurrency Control Study

XML has gained great popularity in recent years and emerged as a new standard for data representation and exchange under, especially, by the promotion of W3C and leading computer companies. XML is being used in more and more areas. With the rapid adoption of XML, the Internet has be turned into a gigantic database gradually.With the increase of the amount of data available in XML, information management techniques for XML data become especially demanding. Today most relational, object-oriented or object-relational DBMS has provided extensions for XML. And at the same time, the database tailored for XML, namely XML native database, gains more and more attention of both researchers and producers. However, from a database point of view, all native XML databases today are far from perfect. Among all of the deficiencies, transaction management and concurrency control technique is one of the biggest ones. In this situation, it's of great importance that we investigate the transaction model and concurrency control technique for XML.First, we propose a general XML transaction model. In contrast to other transaction models, the model we presented treats XML document and path indices in the same way, and we proposed a unified operation model which can describe several access methods, such as DOM, XPath and searching via path indices. We then give a thorough analysis of the complexity with different characteristic of operations. Based on the result, we then propose a concise core operation model, which can be implemented easily and guarantees high concurrency as well. We also distinguish between weak serializability and strong serializability, for order insensitive and order sensitive applications respectively.Based on the transaction model we proposed, we designed two concurrency control protocols, namely MSPX-w and MSPX-s. MSPX-w is for weak serializ-abitily and MSPX-s is for strong serializability. We integrated the strongpoint of multiversioning and semantic concurrency control into these two protocols. Withthe employment of several notable features such as path lock and range lock, the MSPX series of protocols can guarantee good concurrency, without bring too much complexity and burden to the system.Finally, we propose the adaptive lock granularity scheduler, which is a innovative technique that can reduce lock operations and the memory used for maintaining lock objects. First, we designed a concrete lock protocol based on subtree locking. And secondly, we give the formal theory of adaptive lock granularity scheduler, which extends this technique into its general form.We also conducted plenty of evaluations. The result shows that the MSPX series of protocols we proposed can reduce transaction rollbacks and increase system throughput. It also shows the power of the adaptive lock granularity scheduler in case of typical XML environment that the data is hierarchical.