Research On Concurrency Control For XML Database

The research of XML transaction processing today are far from perfect. While some researchers have proposed some concurrency control protocols. The concurrency transaction of multi-users' accessing XML databases and how to advance its efficiency has become an important research subject. A universal perspective suggests that the XML document can be projected into traditional databases so that the perfect transaction mechanism of traditional databases can be used to ensure the mufti-users concurrency of XML. But in fact, because of the conflict between the inborn complanation of traditional databases and the hierarchy of the XML document data, the concurrency mechanism based on the perspective hereinbefore can't support the concurrency access of multi-users to a single XML document high effectively. On the other hand, in the field of Native XML Databases (NXD) the research concerning the transaction and the concurrency control mechanism is initiated not long ago. Currently, although many of NXD claim to support the transaction management, they can't effectively support the concurrency of mufti-users since the granularity of the lock is generally big, that is, it fits the whole document, not the fragment of the document, so the degree of concurrency is relatively slow.In this paper, we propose a concurrency control mechanism of XML database, which based on XPath language. The contributions of this paper are as follows:1. The definition of XML document and the definition of XML transaction model are given, and this paper discusses four manipulations such as querying,inserting,updating and deleting under this model;2. XPLock protocol and rules are defined. We discuss the flow of concurrency control and algorithms of applying lock and releasing lock. The concurrency schedule in this protocol mechanism is proved to be a serializable schedule.3. The detecting and proposing ways for dead lock are given, besides, we present the ways of rollback or abort of a transaction.4. We integrate the multiusers' transaction concurrency and the structure of XML document and use extended preorder numbering schema which supports transaction management to realize the updating of XML document, and achieve the concurrency control of XML.At last some related experiments are done, which focuses on this concurrency control mechanism. The results have proved that the XPLock is efficient for XML concurrency control in degree of concurrency and lock granularity.