Showing papers by "Allel Hadjali published in 2008"

Database preferences queries: a possibilistic logic approach with symbolic priorities

Abstract: The paper presents a new approach to database preferences queries, where preferences are represented in a possibilistic logic manner, using symbolic weights. The symbolic weights may be processed without assessing their precise value, which leaves the freedom for the user to not specify any priority among the preferences. The user may also enforce a (partial) ordering between them, if necessary. The approach can be related to the processing of fuzzy queries whose components are conditionally weighted in terms of importance. Here, importance levels are symbolically processed, and refinements of both Pareto ordering and minimum ordering are used. The representational power of the proposed setting is stressed, while the approach is compared with database Best operator-like methods and with the CP-net approach developed in artificial intelligence. The paper also provides a structured and rather broad overview of the different lines of research in the literature dealing with the handling of preferences in database queries.

Towards fuzzy query answering using fuzzy views - a graded-subsumption-based approach

Abstract: This paper deals with fuzzy query processing in a distributed database context In the framework considered, user queries and view descriptions may include fuzzy predicates A satisfaction threshold is also associated with any user query The idea is to match a fuzzy query against the fuzzy views in order to select only the views that will provide answers whose satisfaction degree is over the threshold specified by the user The main tool for achieving this task is a graded subsumption mechanism, based on a fuzzy implication, which is discussed in a detailed way

First balance sheet of a formal approach in the teaching of Data Structures

Abstract: A formal method, eb, inspired by B method, has been used for the rst time for teaching \data structures". Starting on one hand from a set oriented specication of an abstract type and on the other from the specication of an implementation, method eb favours the calculation of the representation of concrete operations. We present the principle of this approach as well as several examples. The context of its application in a data structures teaching module is then detailed. A rst balance sheet is drawn up.

On the Versatility of Fuzzy Sets for Modeling Flexible Queries

Abstract: The idea of introducing preferences into queries is gaining more and more attention in the database community. After some initial works in the 1970s and 1980s, such as nearest neighbors (Friedman, Baskett, & Shustek, 1975), Deduce2 (Chang, 1982), Preferences (Lacroix & Lavency, 1987), Ares (Ichikawa & Hirakawa, 1986), and Vague (Motro, 1988), a new stream of work, including top-k queries (Bruno, Chaudhuri, & Gravano, 2002), PreferenceSQL (Kie�ling&Köstler,2002),Skyline (B�rzs�nyi, Kossmann, & Stocker, 2001), and the synthesis in Chomicki (2003), is based on the use of preferences inside user queries. Undoubtedly, this contributes to make queries (and database systems) more flexible, but it must be noticed that most (not to say all) of these approaches or systems do not call on fuzzy sets. We believe that the main advantage for founding flexible queries on fuzzy sets lies in the generality of the approach, which allows notably the combination of preferences AbstrAct

Cooperative answering to flexible queries via a tolerance relation

Abstract: One of the common problems that users are confronted with in their web data retrieval is overabundant answers, that is, being provided with an avalanche of responses that satisfy their queries. Most users are overwhelmed by such responses since it is difficult to examine them. In this paper, we attempt to address this issue in the context of flexible queries. The basic idea behind the solution proposed consists in modulating the fuzzy conditions involved in the user query by applying an appropriate transformation. This operation aims at intensifying the constraints of the query to make it more demanding. A transformation that relies on a convenient tolerance relation is introduced. The main features of our proposal are investigated as well.

La notion de division tolérante et son intérêt pour remédier aux réponses vides

Abstract: In this paper, queries involving preferences are considered. Preferences are conveyed thanks to fuzzy predicates whose truth values are a matter of degree. In this framework, the result of a query is no longer a flat set of elements and each component of the answer is assigned a level of satisfaction. However, if such answers are expected to be more satisfactory from a user point of view, empty answers may still occur. The focus of the paper is put on empty answers to queries involving a division, operator which plays a central role far beyond relational database systems, especially in information retrieval systems or Web searches. In the case of an empty answer, the approach suggested here is to weaken the division and different rationales for that are proposed and discussed. It is worth mentioning that most of these weakening mechanisms are also valid for the division of regular relations.