Tractable Concept Languages
نویسندگان
چکیده
Abst rac t We present two concept languages,, called PL1 and PL2 which are extensions of TC. We prove that the subsumption problem in these languages can be solved in polynomial time. Both languages include a construct for expressing inverse roles, which has not been considered up to now in tractable languages. In addition, PL1 includes number restrictions and negation of primitive concepts, while Pl2 includes role conjunction and role chaining. By exploiting recent complexity results, we show that none of the constructs usually considered in concept languages can be added to PL1 and PL2 without losing tractabtlity. Therefore, on the assumption that Languages are characterized by the set of constructs they provide, the two languages presented in this paper provide a solution to the problem of singling out an optimal trade-off between expressive power and computational complexity.
منابع مشابه
Concept Languages as Query Languages
We study concept languages (also called terminological languages) as means for both defining a knowledge base and expressing queries. In particular, we investigate on the possibility of using two different concept languages, one for asserting facts about individual objects, and the other for querying a set of such assertions. Contrary to many negative results on the complexity of terminological...
متن کاملIs PL2 a Tractable Language?
It is believed by the scientific community that PL1 and PL2 are the largest concept languages for which there exists a polynomial algorithm that solves the subsumption problem. This is due to Donini, Lenzerini, Nardi, and Nutt, who have presented two tractable algorithms that are intended to solve the subsumption problem in those languages. In contrast, this paper proves that the algorithm for ...
متن کاملTractable Feature Generation Through Description Logics with Value and Number Restrictions
In the line of a feature generation paradigm based on relational concept descriptions, we extend the applicability to other languages of the Description Logics family endowed with specific language constructors that do not have a counterpart in the standard relational representations, such as clausal logics. We show that the adoption of an enhanced language does not increase the complexity of f...
متن کاملGeneralising tractable VCSPs defined by symmetric tournament pair multimorphisms
We study optimisation problems that can be formulated as valued constraint satisfaction problems (VCSP). A problem from VCSP is characterised by a constraint language, a fixed set of cost functions taking finite and infinite costs over a finite domain. An instance of the problem is specified by a sum of cost functions from the language and the goal is to minimise the sum. We are interested in t...
متن کاملConstructing Constraints
It is well-known that there is a trade-oo between the expressive power of a constraint language and the tractability of the problems it can express. But how can you determine the expressive power of a given constraint language, and how can you tell if problems expressed in that language are tractable? In this paper we discuss some general approaches to these questions. We show that for language...
متن کامل