@conference{Borning89,
author = "A. Borning and M. Mahert and A. Martindale and M. Wilson",
booktitle = "Int. conf. on logic programming",
keywords = "CSP, CLP, HCLP, preferences, satisfaction partielle,
                   optimisation",
pages = "149-164",
title = "{C}onstraint hierarchies and logic programming",
year = "1989",
}