On the Top-k Retrieval Problem for Ontology-Based Access to Databases

The chapter is a succinct summary on the problem of evaluating ranked top-k queries in the context of ontology-based access over relational databases. An ontology layer is used to define the relevant abstract concepts and relations of the application domain, while facts with associated score are stored into a relational database. Queries are conjunctive queries with ranking aggregates and scoring functions. The results of a query may be ranked according to the score and the problem is to find efficiently the top-k ranked query answers.