Research On Concurrency Control Technology Of Native XML Database

With the development of Internet, XML has gained great popularity in recent years andemerged as a new standard for data representation and exchange. XML is being used in moreand more areas. With the rapid adoption of XML, the Internet has been turned into a giganticdatabase gradually. The occurrence of the XML documents that are based on the applicationof Internet or Web, especially, the advent of Native XML Databases (NXD), arises anunprecedented challenge to traditional database field.Concurrency control is the most important mechanism of improving the transactioncapability of database system. And it is also a difficulty in the field of NXD. The researches ofXML transaction processing today are far from perfect. On the problem of how to solveconcurrency control of XML data, a universal perspective suggests that the XML documentcan be projected into traditional databases so that the perfect transaction mechanism oftraditional 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 thehierarchy of the XML document data, the concurrency mechanism based on the perspectivehereinbefore can't control the concurrency access of multi-users to single document higheffectively. On the other hand, in the field of NXD the research concerning the transaction andthe concurrency control mechanism is initiated not long ago. Currently, although many ofNXD claim to support the transaction management, they can't effectively support theconcurrency of multi-users since the granularity of the lock is generally big, that is, it fits thewhole document, not the fragment document.In this paper, we defined an XML transaction model by combining the characteristic ofXML document and simplifying the standard XPath data model. On the base of that, wedesigned a new XPath-based locking protocol and discussed its operational process andalgorithms, detecting and handling methods of dead lock and ways of rollback or abort of atransaction in detail. Then we put forward an extensible encoding schema which can supportXML transaction model, besides, we also made a demonstration of the protocol'sserializability. At last, we proposed a read-only XMLmulti-version protocol by integrating the characteristic of XML applications. It applies multi-version concurrency control of traditionalrelation database to NXD. Because of the read-only transaction never blocks with theupdating transaction each other and doesn't also need any locks, it can increase concurrencyof transactions. Moreover, we made a demonstration of its serializability in the end.In order to validate the effectivity of the protocols and algorithms we proposed in thispaper, we conducted plenty of experiments. The result shows that the protocols we proposedcan reduce transaction rollbacks, increase system throughput and improve performanceeffectively. They also have important significance for future studies and practical applications.