一种基于DTD的XML索引方法

DTD-Based XML Indexing

路径查询是XML查询的一个主要特征,现已提出了多种XML索引方法.DTD的结构信息对于XML索引的建立及查询效率的提高很重要,但现有的大部分索引方法没有利用DTD这一有效资源.提出一种利用DTD的XML索引方法--DBXI(DTD-based XML indexing),该方法采用了新的编码方法,可使路径查询具备如下特征:对于由N个元素／属性组成的具有1个谓词约束的路径表达式,DBXI处理每个XML文档仅需0次或1次元素／属性结点集的结构连接操作;对于在XML文档中不存在匹配结构的路径查询,DBXI能够在比现有的XML索引方法较短的时间内给出无查询结果的判断.实验表明,与Lore,SphinX和XISS等索引方法相比,DBXI能够缩短路径查询的响应时间.

Path expression is a common feature of XML query languages. Many indexing methods have been proposed. DTD can be of great help in XML indexing, but most techniques available now are generic to XML documents that are completely schema-less. Proposed in this paper is DBXI, a new method that takes advantage of information embedded in DTD for speeding up the process of XML path query. DBXI adopts a new coding scheme. With the help of DBXI, a path expression with N elements/attributes and one predicate restriction needs only zero or one structural join operations per XML document. For a path expression that does not match with any paths in XML documents, DBXI can give a judgment of no answer in much shorter time than those of indexing methods in existence. Experimental results demonstrate that DBXI can process path queries faster than Lore, SphinX and XISS do.