Xcerpt: a rule-based query and transformation language for the web [Elektronische Ressource] / von Sebastian Schaffert

Xcerpt: A Rule-Based Query and Transformation Languagefor the WebDissertationzur Erlangung des akademischen Grades desDoktors der Naturwissenschaften¨ ¨an der Fakultat fur Mathematik, Informatik und Statistik¨ ¨der Ludwig-Maximilians-Universitat MunchenvonSebastian SchaffertOktober 2004Erstgutachter: Prof. Dr. Franc¸ois Bry (Universita¨t Mu¨nchen)Zweitgutachter: Prof. Dr. Georg Gottlob (TU Wien)Tag der mu¨ndlichen Pru¨fung: 13. Dezember 2004AbstractThis thesis investigates querying the Web and the Semantic Web. It proposes a new rule-based query language called Xcerpt. Xcerpt differs from other query languages in that it usespatterns instead of paths for the selection of data, and in that it supports both rule chainingand recursion. Rule chaining serves for structuring large queries, as well as for designingcomplex query programs (e.g. involving queries to the Semantic Web), and for modellinginference rules. Query patterns may contain special constructs like partial subqueries, optionalsubqueries, or negated subqueries that account for the particularly flexible structure of data onthe Web.Furthermore, this thesis introduces the syntax of the language Xcerpt, which is illustratedon a large collection of use cases both from the conventional Web and the Semantic Web.In addition, a declarative semantics in form of a Tarski-style model theory is described, andan algorithm is proposed that performs a backward chaining evaluation of Xcerpt programs.