The tradeoff between expressiveness and tractability in Description Logics (DLs) has long been recognised [9]. For DL system designers and implementors there are several possible approaches to this problem [3]. These include: • (severely) constraining expressiveness so that (Tbox) reasoning can be performed in polynomial time (e.g., Classic [11]); • using tractable but incomplete reasoning algo...

Recently, SPARQL-DL was introduced in [7] as a rich query language for OWL-DL ontologies. It provides an OWL-DL-like semantics for SPARQL basic graph patterns which involves as special cases both conjunctive ABox queries and mixed TBox/RBox/ABox queries over Description Logic (DL) ontologies. This paper describes the implementation of a SPARQL-DL query engine and discusses several optimizations...

Classical logics (and hence Description Logics) are monotonic: the set of conclusions increases monotonically with the set of premises. Instead, common-sense reasoning is characterized as non-monotonic: new information can invalidate some of the previously made conclusions. Circumscription is one of the main nonmonotonic formalisms whose idea is to minimize (circumscribe) the extension of given...

Ontologies provide a conceptualization of a domain of interest. Nowadays, they are typically represented in terms of Description Logics (DLs), and are seen as the key technology used to describe the semantics of information at various sites. The idea of using ontologies as a conceptual view over data repositories is becoming more and more popular, but for it to become widespread in standard app...

Two enantiomeric counterparts (l- and d-asparginium cations related by glide planes) are present in the structure of the title compound, C(4)H(9)N(2)O(3) (+)·ClO(4) (-), with a 1:1 cation-anion ratio. The structure is built up from asparginium cations and perchlorate anions. In the crystal, mol-ecules assemble in double layers parallel to (100) through N-H⋯O, O-H⋯O and C-H⋯O hydrogen bonds. In ...