Research On Transaction And Concurrency Control Mechanism For XML Databases

As one of the most basic concepts in the development of databases, transaction has been widely applied in various platforms of the E-commerce and the enterprise's information-based strategy. However, with the tendency of the global network rising, Internet has gradually replaced the operation model of single computer that takes personal computer as a calculating center and become a new standard of the calculating platform. This brings a great change to the application environment of databases. The occurrence of the XML document that is based on the application of Internet or Web, especially, the occurrence of Native XML Databases, arises an unprecedented challenge to traditional databases field.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 multi-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 control the concurrency access of multi-users to single 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 multi-users since the granularity of the lock is generally big, that is, it fits the whole document, not the fragment of the document.The present study aims at presenting a transaction management model of XML databases based on the pseudo-XPath and a controlling mechanism of the multi-users concurrency transaction. The transaction model can be established by defining a data-model of pseudo-XPath containing extending code, and several XML databases operations can be defined on the basis of this transaction model. In accordance with the characteristics of the multi-users concurrency transaction and the structure of the XML document, some algorithms of the path expression guide based on the extending code can be drawn out. On the basis of that, a locking protocol mechanism (XPL) as well as a lock model is suggested, and the process regarding the application, release and update of the lock is illustrated in the paper. Besides, the schedule in this locking protocol mechanism is proved to be a serializable schedule. Consequently, the concurrency control of the multi-users transaction in the XML databases can be achieved.