结构化连接的效率直接影响着XML查询的性能,目前对XML的结构化连接大多都是基于编码的方法.介绍了一种全新的有效支持XML结构化连接的树索引CATI(compact ancestor tree index).CATI的基本思想是,对于给定的一个祖先后代查询(A-D查询)或...结构化连接的效率直接影响着XML查询的性能,目前对XML的结构化连接大多都是基于编码的方法.介绍了一种全新的有效支持XML结构化连接的树索引CATI(compact ancestor tree index).CATI的基本思想是,对于给定的一个祖先后代查询(A-D查询)或Twig查询,遍历XML文档,找出所有的祖先A的实例,用以建立CATI的主干;对于每个A实例,找出它的直接后代D的实例链接在它的后面.因为经典的结构连接算法Stack-Tree算法效率较高且使用较广,因此应用基于CATI的结构连接算法和基于Stack-Tree的结构连接算法就A-D查询和Twig查询做了大量实验.实验结果表明,基于CATI的结构化连接在一般查询情况下性能明显优于基于Stack-Tree的结构化连接.展开更多
As huge volumes of data are organized or exported in tree-structured form, it is quite necessary to extract useful information from these data collections using effective and efficient query processing methods. A natu...As huge volumes of data are organized or exported in tree-structured form, it is quite necessary to extract useful information from these data collections using effective and efficient query processing methods. A natural way of retrieving desired information from XML documents is using twig pattern （TP）, which is, actually, the core component of existing XML query languages. Twig pattern possesses the inherent feature that query nodes on the same path have concrete precedence relationships. It is this feature that makes it infeasible in many actual scenarios. This has driven the requirement of relaxing the complete specification of a twig pattern to express more flexible semantic constraints in a single query expression. In this paper, we focus on query evaluation of partially specified twig pattern （PSTP） queries, through which we can reap the most flexibility of specifying partial semantic constraints in a query expression. We propose an extension to XPath through introducing two Samepath axes to support partial semantic constraints in a concise but effective way. Then we propose a stack based algorithm, pTwigStack, to process a PSTP holistically without deriving the concrete twig patterns and then processing them one by one. Further, we propose two DTD schema based optimization methods to improve the performance of pTwigStack algorithm. Our experimental results on various datasets indicate that our method performs significantly better than existing ones when processing PSTPs.展开更多
Tree Match算法是一种有效的Twig查询匹配算法,但其存在反复分析Twig模式的缺点。针对该问题,引入编译中的部分求值技术,提出一种Twig查询优化方案。通过部分求值提前完成对Twig模式的分析,生成查询专用的指令序列代替原查询程序,并给...Tree Match算法是一种有效的Twig查询匹配算法,但其存在反复分析Twig模式的缺点。针对该问题,引入编译中的部分求值技术,提出一种Twig查询优化方案。通过部分求值提前完成对Twig模式的分析,生成查询专用的指令序列代替原查询程序,并给出查询机执行引擎,从而消除重复计算,优化XML树模式查询过程。实验结果表明,在不同Twig模式下,该优化方案能够有效提高XML查询的执行效率。展开更多
Massive XML data are increasingly generated for the representation, storage and exchange of web information. Twig query processing over massive XML data has become a research focus. However, most traditional algorithm...Massive XML data are increasingly generated for the representation, storage and exchange of web information. Twig query processing over massive XML data has become a research focus. However, most traditional algorithms cannot be directly implemented in a distributed manner. Some of the existing distributed algorithms generate a lot of useless intermediate results and execute many join operations of partial results in most cases; others require the priori knowledge of query pattern before XML partition, storage and query processing, which is impractical in the cases of large-scale data or frequent incoming new queries. To improve efficiency and scalability, in this paper, we propose a 3-phase distributed algorithm DisT3 based on node distribution mechanism to avoid unnecessary intermediate results. Furthermore, we propose a lightweight local index ReP with an enhanced XML partitioning approach using arbitrary partitioning strategy, and based on ReP we propose an improved 2-phase distributed algorithm DisT2ReP to further reduce the communication cost. After the performance guarantees are analyzed, extensive experiments are conducted to verify the efficiency and scalability of our proposed algorithms in distributed twig query applications.展开更多
Finding all occurrences of a twig query in an XML database is a core operation for efficient evaluation of XML queries. It is important to effiectively handle twig queries with wildcards. In this paper, a novel path-p...Finding all occurrences of a twig query in an XML database is a core operation for efficient evaluation of XML queries. It is important to effiectively handle twig queries with wildcards. In this paper, a novel path-partitioned encoding scheme is proposed for XML documents to capture paths of all elements, and a twig query is modeled as an XPattern extended from tree pattern. After definition, simplification, normalization, verification and initialization of the XPattern, both work sets and a join plan are generated. According to these measures, an effiective algorithm to answer for a twig query, called DMTwig, is designed without unnecessary elements and invalid structural joins. The algorithm can adaptively deal with twig queries with branch ([ ]), child edge (/), descendant edge (//), and wildcard (*) synthetically. We show that path-partitioned encoding scheme and XPattern guarantee the I/O and CPU optimality for twig queries. Experiments on representative data set indicate that the proposed solution performs significantly.展开更多
文摘结构化连接的效率直接影响着XML查询的性能,目前对XML的结构化连接大多都是基于编码的方法.介绍了一种全新的有效支持XML结构化连接的树索引CATI(compact ancestor tree index).CATI的基本思想是,对于给定的一个祖先后代查询(A-D查询)或Twig查询,遍历XML文档,找出所有的祖先A的实例,用以建立CATI的主干;对于每个A实例,找出它的直接后代D的实例链接在它的后面.因为经典的结构连接算法Stack-Tree算法效率较高且使用较广,因此应用基于CATI的结构连接算法和基于Stack-Tree的结构连接算法就A-D查询和Twig查询做了大量实验.实验结果表明,基于CATI的结构化连接在一般查询情况下性能明显优于基于Stack-Tree的结构化连接.
基金Supported partially by the National Natural Science Foundation of China (Grant No. 60833005)the National High-Tech Research & Development Program of China (Grant Nos. 2007AA01Z155, 2009AA011904)the National Basic Research Program of China (Grant No.2003CB317000)
文摘As huge volumes of data are organized or exported in tree-structured form, it is quite necessary to extract useful information from these data collections using effective and efficient query processing methods. A natural way of retrieving desired information from XML documents is using twig pattern （TP）, which is, actually, the core component of existing XML query languages. Twig pattern possesses the inherent feature that query nodes on the same path have concrete precedence relationships. It is this feature that makes it infeasible in many actual scenarios. This has driven the requirement of relaxing the complete specification of a twig pattern to express more flexible semantic constraints in a single query expression. In this paper, we focus on query evaluation of partially specified twig pattern （PSTP） queries, through which we can reap the most flexibility of specifying partial semantic constraints in a query expression. We propose an extension to XPath through introducing two Samepath axes to support partial semantic constraints in a concise but effective way. Then we propose a stack based algorithm, pTwigStack, to process a PSTP holistically without deriving the concrete twig patterns and then processing them one by one. Further, we propose two DTD schema based optimization methods to improve the performance of pTwigStack algorithm. Our experimental results on various datasets indicate that our method performs significantly better than existing ones when processing PSTPs.
基金This work is supported in part by the National Natural Science Foundation of China under Grant Nos. 61272181, 61672145, 61572121 and U1401256.
文摘Massive XML data are increasingly generated for the representation, storage and exchange of web information. Twig query processing over massive XML data has become a research focus. However, most traditional algorithms cannot be directly implemented in a distributed manner. Some of the existing distributed algorithms generate a lot of useless intermediate results and execute many join operations of partial results in most cases; others require the priori knowledge of query pattern before XML partition, storage and query processing, which is impractical in the cases of large-scale data or frequent incoming new queries. To improve efficiency and scalability, in this paper, we propose a 3-phase distributed algorithm DisT3 based on node distribution mechanism to avoid unnecessary intermediate results. Furthermore, we propose a lightweight local index ReP with an enhanced XML partitioning approach using arbitrary partitioning strategy, and based on ReP we propose an improved 2-phase distributed algorithm DisT2ReP to further reduce the communication cost. After the performance guarantees are analyzed, extensive experiments are conducted to verify the efficiency and scalability of our proposed algorithms in distributed twig query applications.
基金supported by the National High-Tech Research and Development Plan of China (Grant No.2005AA4Z3030)
文摘Finding all occurrences of a twig query in an XML database is a core operation for efficient evaluation of XML queries. It is important to effiectively handle twig queries with wildcards. In this paper, a novel path-partitioned encoding scheme is proposed for XML documents to capture paths of all elements, and a twig query is modeled as an XPattern extended from tree pattern. After definition, simplification, normalization, verification and initialization of the XPattern, both work sets and a join plan are generated. According to these measures, an effiective algorithm to answer for a twig query, called DMTwig, is designed without unnecessary elements and invalid structural joins. The algorithm can adaptively deal with twig queries with branch ([ ]), child edge (/), descendant edge (//), and wildcard (*) synthetically. We show that path-partitioned encoding scheme and XPattern guarantee the I/O and CPU optimality for twig queries. Experiments on representative data set indicate that the proposed solution performs significantly.
