The paper demonstrates that product configuration applications fit naturally the framework of answer set programming. It is shown that product configuration knowledge can be represented systematically and compactly using a logic program type rule language such that the answers of a configuration task, the configurations, correspond to the models of the rule representation. The paper presents such a rule-bised for realization of a unified configuration ontology using a weight constraint rule language. The language extends normal logic programs with cardinality and weight constraints which leads to a compact and simple formalization. The complexity of the configuration task defined by the formalization is shown to be NP-complete.