In this paper, we analyze the logical definitions of model-based diagnosis recently presented in the literature, and we propose a unified framework (based on the integration of abductive and consistency-based reasoning) in which most of such definitions can be captured. This allows us to single out the existence of a spectrum of alternatives in the logical definition of diagnosis. A lot of attention in the paper is devoted to analyzing the differences among the definitions in the spectrum. In particular, we show that the definitions can be compared on the basis of their restrictiveness and we relate such a restrictiveness with the completeness of the model of the system to be diagnosed. Key words: model-based reasoning, theory of diagnosis, abductive reasoning, consistency-based reasoning.Dans cet article, les auteurs analysent les dkfinitions logiques de diagnostics bases sur un modtle dont il a kte question rkcemment dans certains ouvrages. 11s proposent un cadre unifie (bask sur I'intkgration du raisonnement abductif et du raisonnement base sur la consistance) B I'interieur duquel la plupart de ces definitions peuvent Otre regroupees. %ette particularit6 permet de mettre en lumitre I'existence d'un spectre d'alternatives dans la definition logique du diagnostic.Cet article accorde une attention toute particulikre B I'analyse des diffkrences entre les dkfinitions du spectre. En outre, les auteurs dkmontrent que les definitions peuvent 2tre comparkes en fonction de leur caracttre restrictif, qui est ensuite mis en relation avec la complktude du modkle du systtme faisant I'objet d'un diagnostic.Mots clPs : raisonnement bask sur un modtle, thtorie du diagnostic, raisonnement abductif, raisonnement base sur la consistance.

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Abstract.This paper aims to demonstrate that the principles of adaptation and user modeling, especially social annotation, can be integrated fruitfully with those of the Web 2.0 paradigm and thereby enhance in the domain of cultural heritage. We propose a framework for improving recommender systems through exploiting the users tagging activity. We maintain that Web 2.0's participative features can be exploited by adaptive web-based systems in order to enrich and extend the user model, improve social navigation and enrich information from a bottom-up perspective. Thus our approach stresses social annotation as a new and powerful kind of feedback and as a way to infer knowledge about users. The prototype implementation of our framework in the domain of cultural heritage is named iCITY. It is serving to demonstrate the validity of our approach and to highlight the benefits of this approach specifically for cultural heritage. iCITY is an adaptive, social, multi-device recommender guide that provides information about the cultural resources and events promoting the cultural heritage in the city of Torino. Our paper first describes this system and then discusses the results of a set of evaluations that were carried out at different stages of the systems development and aimed at validating the framework and implementation of this specific prototype. In particular, we carried out a heuristic evaluation and two sets of usability tests, aimed at checking the usability of the user interface, specifically of the adaptive behavior of the system. Moreover, we conducted evaluations aimed at investigating the role of tags in the definition of the user model and the impact of tags on the accuracy of recommendations. Our results are encouraging.

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