Dera: a Faceted Knowledge Organization Framework

The availability of a priori knowledge, also called background knowledge, is fundamental for the functioning of semantics based systems. In this paper we introduce a faceted knowledge organization framework called DERA (for Domain, Entity, Relation, Attribute) and describe its implementation inside a system, called UK (for Universal Knowledge) which is extensible and scalable and which allows for fully automated reasoning via a direct encoding into Description Logics (DL). Extendibility and scalability is obtained by allowing the definition of any number of domains, where a domain is taken to be ―an area of knowledge or field of study that we are interested in or that we are communicating about‖. In turn, a domain is organized into a number of facets where a facet is taken to be ―a hierarchy of homogeneous terms describing an aspect of the knowledge being codified, where each term denotes a primitive atomic concept‖. Domains, facets, terms can be added at any time, and the different applications can use any subset of them. The direct encoding of DERA into DL is obtained by allowing only three types of facets (i.e., Entity, Relation, Attribute) which can be directly translated into DL concepts, roles, attributes, or into instances whose properties are encoded using the terms occurring in the facets themselves. The current implementation of UK contains around 377 Domains, out of which 115 are in priority for development, more than 150,000 terms (encoding concepts, relations and attributes), around 10,000,000 instances and more than 93,000,000 axioms codified using the terms codified in the DERA facets.