To ensure completeness Description Logics (DLs) are popular languages for knowledge of the method, the so-called refinement step is used that recomputes representation and reasoning. They are the underlying the abstraction based on new (sound) entailments formalism for the standardized Web Ontology Language obtained from a previous abstraction. This has the added OWL, which is widely used in many application areas. Recent benefit that not only consistency but also the full materialization years have also seen an increasing interest in ontologybased of the ABox can be computed without (rather expensive) data access, where a TBox with background knowledge, explanation computations or repeated consistency often expressed in a DL language, is used to enrich checks. This paper significantly advances the abstraction refinement datasets (ABoxes), which are then accessible via queries.

The paper presents an approach for optimizing the evaluation of SPARQL queries over OWL ontologies using SPARQL's OWL Direct Semantics entailment regime. The approach is based on the computation of lower and upper bounds, but we allow for much more expressive queries than related approaches. In order to optimize the evaluation of possible query answers in the upper but not in the lower bound, we present a query extension approach that uses schema knowledge from the queried ontology to extend the query with additional parts. We show that the resulting query is equivalent to the original one and we use the additional parts that are simple to evaluate for restricting the bounds of subqueries of the initial query. In an empirical evaluation we show that the proposed query extension approach can lead to a significant decrease in the query execution time of up to four orders of magnitude.

In many tasks related to reasoning about consequences of a logical theory, it is desirable to decompose the theory into a number of components with weakly-related or independent signatures. This facilitates reasoning when signature of a query formula belongs to only one of the components. However, an initial theory may be subject to change due to execution of actions affecting features mentioned in the theory. Having once computed a decomposition of a theory, one would like to know whether a decomposition has to be computed again for the theory obtained from taking into account the changes resulting from execution of an action. In the paper, we address this problem in the scope of the situation calculus, where change of an initial theory is related to the well-studied notion of progression. Progression provides a form of forward reasoning; it relies on forgetting values of those features which are subject to change and computing new values for them. We prove new results about properties of decomposition components under forgetting and show when a decomposition can be preserved in progression of an initial theory.