XML query processing

XQuery is starting to gain significant traction as a language for querying and transforming XML data. It is used in a variety of different products. Examples to date include XML database systems, XML document repositories, XML data integation, workflow systems, and publish and subscribe systems. In addition, XPath of which XQuery is a superset is used in various products such as Web browsers. Although the W3C XQuery specification has not yet attained Recommendation status, and the definition of the language has not entirely stabilized, a number of alternative proposals to implement and optimize XQuery have appeared both in industry and in the research community. Given the wide range of applications for which XQuery is applicable, a wide spectrum of alternative techniques have been proposed for XQuery processing. Some of these techniques are only useful for certain applications, other techniques are general-purpose. The goal of this seminar is to give an overview of the existing approaches to process XQuery expressions and to give details of the most important techniques. The presenters have experience from designing and building an industrial-strength XQuery engine [1]. The seminar will give details of that XQuery engine, but the seminar will also give extensive coverage of other XQuery engines and of the state of the art in the research community. The agenda for the seminar is as follows: (1) Introduction to XQuery: Motivation, XQuery data model, XQuery type system, Basic query language concepts; (2) Internal Representation of XML Data: DOM, SAX Events, TokenStream, Skeleton, Vertical Partitioning; (3) XQuery Algebras: XQuery Core vs. Relational Algebra, XQuery Algebras from Research Projects; (4) XPath Query Processing: Transducers, Automata, etc.; (5) XQuery Optimization: XML query equivalence, Rewrite Rules, Cost Models; (6) XQuery Runtime Systems: Iterator Models, Algorithms for XQuery Operators; (7) XML Indexes: Value and path indexes, others; (8) XQuery Products and Prototypes: XQRL/BEA, Galax, Saxon, etc. (as available); (9) Advanced Query Processing Techniques, Related Topics: Querying compressed XML data, Multi-Query Optimization, Publish/Subscribe and XML Information Filter, XML Data Integration, XML Updates, XML integrity constraints; (10) Summary.