Variable-Strength Conditional Preferences for Ranking Objects in Ontologies

We introduce conditional preference bases as a means for ranking objects in ontologies. Conditional preference bases consist of a description ogic knowledge base and a finite set of conditional preferences, which are statements of the form “generally, in the context φ, property α is referred over property ¬α with strength s”. They are inspired by variable-strength defaults in conditional knowledge bases. We define the notion f consistency for conditional preference bases, and we show how consistent conditional preference bases can be used for ranking objects in ntologies, where every object represents essentially a set of individuals that are sharing the same ranking-relevant properties. More concretely, e define two object rankings, denoted κsum and κlex, which evaluate the strengths of conditional preferences in an additive and a lexicographic ay, respectively. Furthermore, we provide algorithms for the main computational tasks for ranking objects under conditional preference bases, e analyze the complexity of these tasks, and we delineate a tractable special case. To give evidence of the usefulness of this approach in practice, e describe two applications in the areas of product and literature search, where it allows especially for a flexible user-defined ranking of the query esults reflecting personal preferences. 2007 Elsevier B.V. All rights reserved.