| XML, Extensible Markup Language, has actually become the data transmission standard in the Internet. And how to effectively store and query these data is a hot topic of research in academia now. Structural Join method is the core operation in querying XML data.To effectively support structural query, various encoding schemes have been proposed.Global region encoding scheme is convenient to judge the structural relationship, and was widely used in structural join algorithms. Nevertheless, the efficiency of XML document which is encoded by Global region encoding scheme is updated poor. Relatively, can make use of local region encoding scheme to solve documents'updating, but it does not directly support the structural relationship of nodes'judgment, and hence can not be used by structural join algorithms. As a combination of the two, prefix encoding scheme which support to judge nodes'structural relationship and has good file updating efficiency is a promising encoding scheme.To further enhance the efficiency of documents'updating, base on the classic Dewey encoding scheme, provides an expansion of the Dewey encoding scheme named Ext-Dewey. When updating a document encoded by Ext-Dewey, no other nodes in the tree need be re-encoded. Further more, designed the structural join algorithm based on Ext-Dewey encoding scheme, and in the algorithm matching father-child relationship, the non-use of stack which is commonly used by classic algorithms to preserve intermediate results can reduce space costs. In response region encoding scheme to achieve a optimize algorithms, and there is no need to use any index structure, can in some cases avoid unnecessary linking operation, and enhance the efficiency of algorithms. Finally, use this strategy to the algorithm based on the Ext-Dewey encoding scheme.The experimental data indicate that the algorithm based on Ext-Dewey encoding scheme is correct and the algorithms be optimized outperforms that before a general improvement. |
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