On Three Classes of Division Queries Involving Ordinal Preferences

摘要

In this paper, we are interested in taking preferences into account for a family of queries inspired by the relational division. A division query aims at retrieving the elements associated with a specified set of values and usually the results remain not discriminated. So, we suggest the introduction of preferences inside such queries with the following specificities: ⅰ) the user gives his/her preferences in an ordinal way and ⅱ) the preferences apply to the divisor which is defined as a hierarchy of sets. Different uses of the hierarchy are investigated, which leads to queries conveying different semantics and the property of the result in terms of a quotient is studied. A special attention is paid to the implementation of such queries using a regular database management system and some experimental results illustrate the feasibility of the approach.