Section: Research Program

Elements on Knowledge Systems and Semantic Web

Keywords:

knowledge representation, ontology, description logics, classification-based reasoning, case-based reasoning, semantic web, information retrieval

Usually, people try to take advantage of the web by searching for information (navigation, exploration), and by querying documents using search engines (information retrieval). Then people try to analyze the obtained results, a task that may be difficult and tedious. Semantic web is an attempt for guiding search for information with the help of software agents, that are in charge of asking questions, searching for answers, classifying and interpreting the answers. However, a software agent may be able to read, understand, and manipulate information on the web, if and only if the knowledge necessary for achieving those tasks is available. This is why ontologies are of main importance with respect to the task of setting up semantic web. Thus, there is a need for representation languages for annotating documents, describing the content of documents and giving a semantics to this content. Knowledge representation languages are good candidates for achieving the task: they have a syntax with an associated semantics, and they can be used for retrieving information, answering queries, and reasoning.

Semantic web constitutes a good platform for experimenting ideas on knowledge representation, reasoning, and KDDK. In particular, the knowledge representation language used for designing ontologies is the OWL language, which is based on description logics (DLs [79] ). In OWL, knowledge units are represented within concepts (or classes), with attributes (properties of concepts, or relations, or roles), and individuals. The hierarchical organization of concepts (and relations) relies on a subsumption relation (i.e. a partial ordering).

The inference services are based on subsumption, concept and individual classification, two tasks related to “classification-based reasoning”. Furthermore, classification-based reasoning can be extended into case-based reasoning (CBR), which relies on three main operations: retrieval, adaptation, and memorization. Given a target problem, retrieval consists in searching for a source (memorized) problem similar to the target problem. Then, the solution of the source problem is adapted to fulfill the constraints attached to the target problem, and possibly memorized for further reuse.

Still in the context of semantic web, research work is also carried on semantic wikis which are web sites for collaborative editing, in which documents can be annotated thanks to semantic annotations and typed relations between wiki pages. Such links provide kind of primitive knowledge units that can be used for guiding information retrieval or knowledge discovery.