Lock-based Concurrency Control for XML Document Models

Abstract

XML has become the most important technique to exchange data in WWW. Providing efficient access to XML document databases is thus crucial. Concurrency control protocols allow transactions to be executed concurrently to improve performance. In XML, XPath and DOM (Document Object Model) are two widely used models to access XML documents. XPath is a language to locate nodes in XML documents. DOM provides an interface allowing programs to dynamically access and update both the content and structure of XML documents. XPath reveals finer access behavior than DOM, but DOM provides a more convenient interface to access XML documents. Based on XPath and DOM, we propose and compare two lock-based concurrency control protocols for XML documents, called XLP and DLP, respectively. DLP is an extension of our former research on XLP [7]. Both of them have the features of richer lock modes, refined lock granularity, lower lock conflict and lock conversion. Our simulation results show that, for XML documents of different sizes, XLP outperforms DLP by 109.24% on average. Other performance comparison between XLP and DLP is also made in this study for various transactions with different destination node sizes and read/write ratios.