The use of carin language and algorithmsfor

PICSEL is a project 1 aiming at building information servers over existing information sources that are distributed and possibly heteregeneous. The approach which has been chosen in PICSEL is to deene an information server as a knowledge-based mediator in which carin is used as the core logical formalism to represent both the domain of application and the contents of information sources that are available and relevant to the domain of application. The goal of this paper is to point out the way we exploit the expressive power of carin for describing the contents of information sources in a way that enables avoiding the query reformulation problem, by mixing the local-as-global and global-as-local approaches. We illustrate it on examples coming from the tourism domain, which the rst real case that we have to consider in PICSEL in collaboration with the Web (and Minitel) travel agent Degriftour 2. 11.1 Introduction In recent years, the problem of information integration has received a lot of attention. In particular, several information integration systems (e.g, Information Manifold 18], TSIMMIS 6], SIMS 2], Infomaster 7]) have been proposed, based on a knowledge-based mediator architecture. They have in common the use of a logical formalism to describe both the domain model and the contents of the information sources. They diier by (i) the speciic logical formalism that they are based on, (ii) the way they express the contents of the information sources, and (iii) the query processing that they perform. As pointed out in 16] two approaches can be distinguished depending on the mapping between the domain relations (called the global relations) and the sources relations (called the local relations) which represent the contents and capabilities of the information sources. In the local-as-global approach, illustrated by Information Manifold 18] or Infomaster 7], the local relations are deened as views over global relations. In the global-as-local approach, illustrated by TSIMMIS 6], the mapping is done from the global relations to the local relations: the local relations are considered as as many new base predicates in term of which some global relations can be expressed. The 1 granted by CNET (Centre National d'Etudes des Telecommunications) under contract number 97 1B 378 2 see