Relaxing Ceteris Paribus Preferences with Partially Ordered Priorities

Conditional preference networks (CP-nets) are a simple approach to the compact representation of preferences. In spite of their merit the application of the ceteris paribus principle underlying them is too global and systematic and sometimes leads to questionable incomparabilities. Moreover there is a natural need for expressing default preferences that generally hold, together with more specific ones that reverse them. This suggests the introduction of priorities for handling preferences in a more local way. After providing the necessary background on CP-nets and identifying the representation issues, the paper presents a logical encoding of preferences under the form of a partially ordered base of logical formulas using a discrimin ordering of the preferences. It is shown that it provides a better approximation of CP-nets than other approaches. This approximation is faithful w.r.t. the strict preferences part of the CP-net and enables a better control of the incomparabilites. Its computational cost remains polynomial w.r.t. the size of the CP-net. The case of cyclic CP-nets is also discussed.