Patterns and Types for Querying XML Documents

Abstract

Among various proposals for primitives for deconstructing XML data two approaches seem to clearly stem from practise: path expressions, widely adopted by the database community, and regular expression patterns, mainly developed and studied in the programming language community. We think that the two approaches are complementary and should be both integrated in languages for XML, and we see in that an opportunity of collaboration between the two communities. With this aim, we give a presentation of regular expression patterns and the type systems they are tightly coupled with. Although this article advocates a construction promoted by the programming language community, we will try to stress some characteristics that the database community, we hope, may find interesting.

N-Ary Queries by Tree Automata

“…Beside other applications, node selection is basic to XML transformation languages (Query, XSLT, XDuce, CDuce, tree transducer, etc [13,7,15]) and of interest for Web information extraction (Lixto, Squirrel, etc [1,12,5]). …”

“…Monadic Datalog yields attractive alternatives for expressing monadic queries, in particular for visual Web information extraction [11]. More general n-ary queries have been promoted by XML programming languages with pattern matching such as XDuce and CDuce [13,7]. Their patterns or types with n capture variables specify n-ary node selection queries in trees.…”

Pattern Matching and Bisimulation

“…One interesting path of further development is to introduce types into CPC and extend the pattern unification mechanism by taking types into account, as done e.g. in [9]. The study of typed equivalences would then be the most natural path to follow, by combing the theory in this paper with the assumed types.…”

A Typed Calculus for Querying Distributed XML Documents

“…Types take the form of a tree grammar. [11] or the review in [5], we define patterns by extending types with capture variables. Patterns are used for inspecting documents and extracting information.…”