Transaction management in RDBMSs with XML support
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The wide use of XML as a description format for semistructured data resulted in the development of XML data management facilities for the existing relational database management systems (RDBMSs). The leading vendors of RDBMSs have included the support of the XML query and update languages in their systems. However, because of considerable differences between the relational and XML data models, transaction management methods in RDBMS are not quite appropriate for XML data. A series of our experiments with RDBMSs with XML support have revealed that, when accessing the same XML document for reading and updating, the transactions are executed sequentially, although they do not conflict. Thus, concurrency of XML transactions in RDBMSs is essentially limited. In the paper, a new method of the XML transaction management in RDBMSs is described. Our method is based on a two-level transaction model. The key component of this model is the new concurrency control protocol, called XDGL, especially tailored for synchronization of the XML transactions. The XDGL protocol is implemented on the top of the existing RDBMS transaction manager. A software prototype of the suggested method has been implemented for Microsoft SQL Server 2005. Our experiments have revealed considerable reduction of the XML transaction execution time when the number of parallel queries and updates is large.
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