A Full Pattern-Based Paradigm for XML Query Processing

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.

Very Large Data Bases, 2006

XQuery and SQL/XML are powerful new languages for querying XML data. However, they contain a number of stumbling blocks that users need to be aware of to get the expected results and performance. For example, certain language features make it hard if not impossible to exploit XML indexes. The major database vendors provide XQuery and SQL/XML support in their current or upcoming product releases. In this paper, we identify common pitfalls gleaned from the experiences of early adopters of this functionality. We illustrate these pitfalls through concrete examples, explain the unexpected query behavior, and show alternative formulations of the queries that behave and perform as anticipated. As results we provide guidelines for XQuery and SQL/XML users, feedback on the language standards, and food for thought for emerging languages and APIs.

2000

In this paper, we describe the characteristics of two different query languages designed to query XML data: DSQL, a declarative SQL like language and XQuery, a procedural language that is fast becoming the defacto language for XML querying. We then describe the design of an experiment aimed at comparing the accuracy and efficiency of the query formulation process when using

Lecture Notes in Computer Science, 2003

Most query and transformation languages developed since the mid 90es for XML and semistructured data-e.g. XQuery [1], the precursors of XQuery [2], and XSLT [3]-build upon a path-oriented node selection: A node in a data item is specified in terms of a root-to-node path in the manner of the file selection languages of operating systems. Constructs inspired from the regular expression constructs * , +, ?, and "wildcards" give rise to a flexible node retrieval from incompletely specified data items. This paper further introduces into Xcerpt, a query and transformation language further developing an alternative approach to querying XML and semistructured data first introduced with the language UnQL [4]. A metaphor for this approach views queries as patterns, answers as data items matching the queries. Formally, an answer to a query is defined as a simulation [5] of an instance of the query in a data item.

Lecture Notes in Computer Science, 2006

As XML applications become more complex, there is a growing interest in extending XQuery with side-effect operations, notably XML updates. Unfortunately, the presence of side-effects is at odds with XQuery's declarative semantics which favors optimization. In this paper, we propose a semantic framework that enables extending XQuery with side-effect operations, while preserving the benefits of XQuery's declarative semantics when possible. We use that framework to define "XQuery!", an extension of XQuery 1.0 that supports first-class XML updates and user-level control over update application. We show that those extensions can be easily implemented within an existing XQuery processor and how to recover basic database optimizations for such a language.

2002

Abstract This paper proposes XAL, an XML ALgebra. Its novelty is based on the simplicity of its data model and its well-defined logical operators, which makes it suitable for composability, optimizability, and semantics definition of a query language for XML data. At the heart of the algebra resides the notion of collection, a concept similar to the mathematician's monad or functional programmer's comprehension.

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).

International Journal of Web Information Systems, 2008

PurposeEfficient processing of XML queries is critical for XML data management and related applications. Previously proposed techniques are unsatisfactory. The purpose of this paper is to present Determined – a new prototype system designed for XML query processing and optimization from a system perspective. With Determined, a number of novel techniques for XML query processing are proposed and demonstrated.Design/methodology/approachThe methodology emphasizes on query pattern minimization, logic‐level optimization, and efficient query execution. Accordingly, three lines of investigation have been pursued in the context of Determined: XML tree pattern query (TPQ) minimization; logic‐level XML query optimization utilizing deterministic transformation; and specialized algorithms for fast XML query execution.FindingsDeveloped and demonstrated were: a runtime optimal and powerful algorithm for XML TPQ minimization; a unique logic‐level XML query optimization approach that solely pursues...

Computer Networks, 1999

An important application of XML is the interchange of electronic data (EDI) between multiple data sources on the Web. As XML data proliferates on the Web, applications will need to integrate and aggregate data from multiple source and clean and transform data to facilitate exchange. Data extraction, conversion, transformation, and integration are all well-understood database problems, and their solutions rely on a query language. We present a query language for XML, called XML-QL, which we argue is suitable for performing the above tasks. XML-QL is a declarative, 'relational complete' query language and is simple enough that it can be optimized. XML-QL can extract data from existing XML documents and construct new XML documents.

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.