XTQ: A Declarative Functional XML Query Language

Various query languages have been proposed to extract and restructure infor-mation in XML documents. These languages, usually claiming to be declar-ative, mainly consider the conjunctive relationships among data elements.In order to present the operations where the hierarchical and the disjunc-tive relationships need to be considered, such as restructuring hierarchy andhandling heterogeneity, the programs in these languages often exhibit a pro-cedural style and thus the declarativeness in them is not so prominent as inconventional query languages like SQL.In this paper, we propose a declarative pattern-based functional XMLquery language named XML Tree Query (XTQ). XTQ adopts expressivecomposite patterns to present data extraction, meanwhile establishing theconjunctive, the disjunctive and the hierarchical relationships among dataelements. It uses the matching terms, a composite structure of the variablesbound to the matched data elements, to present a global sketch of the exThis research is partially supported by National Science Foundation of China andOpen Foundation of State Key Lab of Software Engineering.The authors wish to thank the anonymous referees for their valuable comments andsuggestions, which greatly improved the technical content and the presentation of thepaper. Also thanks to Tieyun Qian and Ming Zhong for their valuable advice and effortsin revising the submission.Corresponding AuthorEmail addresses: [email protected] (Xuhui Li), [email protected](Mengchi Liu), [email protected] (Shanfeng Zhu), [email protected] (ArifGhafoor) Preprint submitted to arXiv.orgJune 6, 2014 tracted data, and develops a deductive restructuring mechanism of matchingterms to indicate data transformation, especially for restructuring hierar-chy and handling heterogeneity. Based on matching terms, XTQ employsa coherent approach to function declaration and invocation to consistentlyextract and construct composite data structure, which integrates features ofconventional functional languages and pattern-based query languages. Addi-tionally, XTQ also supports data filtering on composite data structure suchas hierarchical data, which is seldom deliberately considered in other studies.We demonstrate with various examples that XTQ can declaratively presentcomplex XML queries which are common in practice.