Querying semistructured data using a rule-oriented XML query language

The goal of the paper is to propose a semistructured data model for representing XML documents and a language for querying semistructured database representing XML data. The language is based on a path calculus and on its extension involving rules (in Datalog style) and Skolem functions. Three kinds of matching between query variables and database objects are discussed: a rigid, semirigid, and flexible matching. The flexible matching is of special importance since semistructured data does not conform to a rigid schema, its structure is often not known in advance and its structure may change frequently. We propose a method, which is based on regular path expressions, supporting valuation of query variables according to those three kinds of matching. The containment problem for this matchings is discussed. The main idea of an experimental implementation is outlined.