A method to assign the nodes of a tree a number or a bit string, which reflects some relationshiops among the nodes and can be used to facilitate computation.
Published in Chapter:
A New Algorithm for Minimizing Tree Pattern Queries
Yangjun Chen (University of Winnipeg, Canada)
Copyright: © 2009
|Pages: 9
DOI: 10.4018/978-1-59904-845-1.ch079
Abstract
XML employs a tree-structured model for representing data. Queries in XML query languages, for example, XPath (World Wide Web Consortium, 1999), XQuery (World Wide Web Consortium, 2001), XML-QL (Deutch, Fernandex, Florescu, Levy, & Suciu, 1999), and Quilt (Chamberlin, Clark, Florescu, & Stefanescu 1999; Chamberlin, Robie, & Florescu, 2000), typically specify patterns of selection predicates on multiple elements that have some specified tree structured relationships. For instance, the following XPath expression: a[b[c and //d]]/b[c and e//d] asks for any node of type b that is a child of some node of type a. In addition, the b-node is the parent of some c-node and some e-node, as well as an ancestor of some d-node. In general, such an expression can be represented by a tree structure as shown in Figure 1(a). In such a tree pattern, the nodes are types from S ? {*} (* is a wildcard, matching any node type), and edges are parent-child or ancestor-descendant relationships. Among all the nodes of a query Q, one is designated as the output node, denoted by output(Q), corresponding to the output of the query.