Walking through the semantics of frame-based description languages a case study

Starting from FL -, the first formal language belonging to the Frame-Based Description Languages (FDL) family, its expressive power is enhanced by adding new conceptand role-forming operators. The possibility of giving roles a structure will be analyzed, allowing conjunction of roles and introducing thereafter functional roles, which allow a simple form of cardinality as well. Moreover, primitive descriptions are discussed for both concepts and roles. The relevant properties of these languages, with respect to increasing expressive power, such as soundness, completeness and computational complexity of the subsumption procedure are presented formally. Beside these features a meaningful aim of our work is to show a methodology for the analysis of an FDL. Therefore in this paper not only the formal properties (the coherence) of the single languages will be explored, but also the relation of these languages with their effective use in a representational framework (the adequacy). It will be shown how an FDL can lose its expected intuitive properties by augmenting expressiveness: some solutions to this problem are proposed, following constructive criteria. This study concludes with a discussion of the language KFL, the formal basis for the Tbox of a KR system currently in use in a natural language project.