XML的并发加锁协议

随着XML数据库管理系统(XML DBMS)研究的日益深入，研究基于树型结构的XML数据的并发控制协议变得十分重要．由Silberschatz和Kedem提出的树加锁协议(tree protocol)是基于静态树结构数据而定义的．而XML数据是动态变化的树型结构数据．针对XML数据的特点，定义了一个操作集，它可以将一个树型结构的XML文档变化为另外一个合法的树型结构的：XML文档．该操作集的最大特点是其操作对象为一棵子树而非一个结点．在这个操作集基础上定义了XML动态树协议XDTP(XML dynamic tree protocol)，并证明了该协议能继续保持静态树协议的优良特性：可串行化(serializability)和无死锁(deadlock-freedom)．在实际的数据集上进行了实验，结果表明XDTP有着较好的性能．

Concurrent Locking Protocols for XML

With the development of research on XML database management systems (XML DBMS),concurrent processing on mass XML data makes it very important to study the concurrency control protocols based on tree-structured XML data. The tree locking protocol,introduced by Silberschatz and Kedem,was defined based on static tree-structured data. However,as is known,XML data items are the dynamically changing tree-structured data. In accordance with the properties of XML data,a set of operations are defined,which can be used to change XML document from one tree-structured form to another legal tree-structured form. The most distinguished feature of this set of operations is that its operating object is a subtree,not a single node of the XML document. This characteristic fits for the XML data very much,because the valuable information of XML document tree all lies in its leaves. Based on this set of operations,an XML dynamic tree protocol (XDTP) is presented and it is proved that this protocol,just like its static counterpart-tree protocol,continues to ensure serializability and deadlock-freedom in the presence of these operations. Experiments are conducted on the DBLP XML data set. The results of these experiments demonstrate that the XML dynamic tree protocol XDTP performs very well in this circumstance.