Put a Tree Pattern in Your Algebra

Lecture Notes in Computer Science, 2005

In this article we investigate a novel execution paradigm-ML-like pattern-matchingfor XML query processing. We show that such a paradigm is well adapted for a common and frequent set of queries and advocate that it constitutes a candidate for efficient execution of XML queries far better than the current XPath-based query mechanisms. We support our claim by comparing performances of XPath-based queries with pattern based ones, and by comparing the latter with the two efficiency-best XQuery processor we are aware of.

This document proposes an algebra for XML Query. The algebra has been submitted to the W3CXM L Query Working Group. A novel feature of the algebra is the use of regular-expression types, similar in power to DTDs or XML Schemas, and closely related to Hasoya, Pierce, and Vouillon’s work on Xduce. The iteration construct involves novel typing rules not encountered elsewhere (even in Xduce).

2005

Popular XML languages, like XPath, use "treepattern" queries to select nodes based on their structural characteristics. While many processing methods have already been proposed for such queries, none of them has found its way to any of the existing "lightweight" XML engines (i.e. engines without optimization modules). The main reason is the lack of a systematic comparison of query methods under a common storage model. In this work, we aim to fill this gap and answer two important questions: what the relative similarities and important differences among the tree-pattern query methods are, and if there is a prominent method among them in terms of effectiveness and robustness that an XML processor should support. For the first question, we propose a novel classification of the methods according to their matching process. We then describe a common storage model and demonstrate that the access pattern of each class conforms or can be adapted to conform to this model. Finally, we perform an experimental evaluation to compare their relative performance. Based on the evaluation results, we conclude that the family of holistic processing methods, which provides performance guarantees, is the most robust alternative for such an environment.

2007

Tree Pattern Queries [7,6] are now well admitted for modeling parts of XML Queries. Actual works only focus on a small subpart of XQuery specifications and are not well adapted for evaluation in a distributed heterogeneous environment. In this paper, we propose the TGV (Tree Graph View) model for XQuery processing. The TGV model extends the Tree Pattern representation in order to make it intuitive, has support for full untyped-XQuery queries, and for optimization and evaluation. Several types of Tree Pattern are manipulated to handle all XQuery requirements. Links between Tree Patterns are called hyperlinks in order to apply transformations on results. The TGV has been implemented in a mediator system called XLive.

2004

Classical logical optimization techniques rely on a logical semantics of the query language. The adaptation of these techniques to XQuery is precluded by its definition as a functional language with operational semantics. We introduce Nested XML Tableaux which enable a logical foundation for XQuery semantics and provide the logical plan optimization framework of our XQuery processor. As a proof of concept, we develop and evaluate a minimization algorithm for removing redundant navigation within and across nested subqueries. The rich XQuery features create key challenges that fundamentally extend the prior work on the problems of minimizing conjunctive and tree pattern queries.

2002

XML queries typically specify patterns of selection predicates on multiple elements that have some specified tree structured relationships. The primitive tree structured relationships are parent-child and ancestor-descendant, and finding all occurrences of these relationships in an XML database is a core operation for XML query processing.

Lecture Notes in Computer Science, 2002

Abstract. Querying XML has been the subject of much recent inves- tigation. A formal bulk algebra is essential for applying database-style optimization to XML queries. We develop such an algebra, called TAX (Tree Algebra for XML), for manipulating XML data, modeled as ...

Proceedings 17th Annual IEEE Symposium on Logic in Computer Science

Monadic query languages over trees currently receive considerable interest in the database community, as the problem of selecting nodes from a tree is the most basic and widespread database query problem in the context of XML. Partly a survey of recent work done by the authors and their group on logical query languages for this problem and their expressiveness, this paper provides a number of new results related to the complexity of such languages over so-called axis relations (such as "child" or "descendant") which are motivated by their presence in the XPath standard or by their utility for data extraction (wrapping).

XML is becoming prevalent in data presentation and data exchange on the internet. One important issue in the XML research community is how to query XML documents to extract and restructure information. Currently, XQuery based on XPath is the most promising standard. In this paper, we discuss limitations of XPath and XQuery, and propose a generalization of XPath called XTree that overcomes these limitations. Using XTree, multiple variable bindings can be instantiated in one expression; and XTree expressions, which represent a tree rather than a path, can be used in both the querying part and the result construction part of a query. Based on XTree, we develop an XTree query language, which is more compact and convenient to use than XQuery, and supports common query operations such as join, negation, grouping, and recursion in a direct way. We describe an algorithm that converts XTree query scripts to XQuery scripts. This algorithm provides not only a means of executing queries written in XTree query language but also highlights differences between the two query languages.

2004

XQuery is the emerging standard for querying XML data sources. XLive is a light XML/XQuery mediator developed at University of Versailles whose engine processes an XML algebra derived from the relational one extended to process in dataflow XML trees. The query optimizer translates a subset of XQuery in this algebra.