Section: Scientific Foundations
Keywords : recommender system, personalization, collaborative filtering, hypermedia, user profile, KDD, CBR, case-based reasoning, experience management, reuse of past experiences, social navigation, search engine, search access, indexing, user behaviour.
Supporting Information Retrieval
Our researches for supporting information retrieval are mainly related to personalization and the following topics:
use and/or construction of user profiles (cf. the projects EPIA (cf. section 7.1.1 ) and Eiffel (cf. section 7.1.3 );
sophisticated interfaces as in the Eiffel project (cf. section 7.1.3 );
query interface and ranking criteria in the context of search engines (cf. section 6.5.6 );
collaborative filtering: see our Broadway approach for designing adaptive recommender systems (cf. section 3.4.1 ) on which are based most of our past and current contracts. See also our software CBR*Tools and Broadway*Tools.
Design of Adaptive Recommender Systems
Information retrieval support tools as recommender systems are very useful in very large information systems. The objective of a recommender system is to help system users to make their choices in a field where they have little information for sorting and evaluating the possible alternatives  ,  ,  .
A recommender system can be divided into three basic entities (cf. Figure 3 ): the group of recommendations producer agents, the module of recommendation computation and the group of recommendations consumers.
A major challenge in the field of recommender systems design is the following: How to produce adaptive recommendations of high quality minimizing the effort of producers and the consumers?
Two main complementary approaches are proposed in the literature: 1) approaches based on the content and the machine learning of user profiles and 2) approaches known as a collaborative filtering based on data mining techniques. The user profile is a structure of data that describes user's topics of interest in the space of the objects which can be recommended. The user profile is a structure built in the first approach or specified by the user in the second approach.
The user profile is used either to filter available objects (content-based filtering), or to recommend a user something that satisfied previous users with a similar profile (collaborative filtering)  .
In the AxIS project, we continue the development of an hybrid approach for recommendations based on the analysis of visited content and on collaborative filtering; User group's past behaviours are used to compute the recommendations (collaborative filtering). This approach is able to support some usage evolutions without complete re-design. Usage analysis of the recommender system itself may be very useful to support designers in a possible re-design or improvement of their IS.
Approaches based on data mining are mainly statistical, where the sequence of events in the history is not taken into account for computing the recommendations. There are some early examples in the field of navigation assistance on the Web: the FootPrints system  and the system of Yan et al.  .
The implementation challenges of our approach relate to the following aspects:
providing techniques of identification and extraction of relevant behaviours (i.e. the learning behaviours or case behaviours) starting from raw data of past behaviours,
defining methods and measures of similarities between behaviours,
defining inference techniques of adaptive recommendations starting from the identified relevant past behaviours (or starting from the reminded cases).
We study the class of recommender systems, based on the re-use of a user group's past experiences, using case based reasoning techniques (CBR). Case-Based Reasoning (CBR) is a problem solving paradigm based on the reuse by analogy of past experiences, called ``cases''. In order to be found, a case is generally indexed according to certain relevant and discriminating characteristics, called ``indices''; these indices determine in which situation (or context) a case can be re-used. Case-Based Reasoning  usually breaks up into four principal phases: retrieve, re-use, revise and retain.
Difficult problems in CBR are related to: definition and representation of a case, organization of the database containing the cases, various used indexing methods and definition of ``good'' similarities measurements for the case search, link between the steps research and adaptation (the best retrieved case being the most easily adaptable case), definition of an adaptation strategy starting with the found case(s), training of new indices, etc.
We focus on two types of recommender systems:
systems where computation of recommendations is based on re-using users group's experiences in searching for information in a Web-like information system on an Internet/Intranet site. These systems aim at providing adaptive assistance to users in their task when searching for information.
systems where the computation of recommendations is based on the re-use of past experts'experiences, in order to assist in the design process.
We explore all the problems previously described by using case-based reasoning (CBR) techniques and more generally KDD techniques.
We pursue the evaluation of our results in CBR, in particular the indexing model by behavioral situation, the object-oriented framework CBR*Tools and toolbox Broadway*Tools in the context of our current contracts EPIA and MobiVip (cf. section 7.1 ). Moreover, we pursue the study of sessions indexing techniques and plan to use some sequential pattern extraction and clustering algorithms for the on-line and off-line analysis of users'Web usage.