ELK: A Reasoner for OWL EL Ontologies

ELK is a specialized reasoner for the lightweight ontology language OWL EL. The practical utility of ELK is in its combination of high performance and comprehensive support for language features. At its core, ELK employs a consequence-based reasoning engine that can take advantage of multi-core and multi-processor systems. A modular architecture allows ELK to be used as a stand-alone application, Protégé plug-in, or programming library (either with or without the OWL API). This system description presents the current state of ELK. 1 The System Overview The logic-based ontology language OWL is becoming increasingly popular in application areas, such as Biology and Medicine, which require dealing with a large number of technical terms. For example, medical ontology SNOMED CT provides formal description of over 300,000 medical terms covering various topics such as diseases, anatomy, and clinical procedures. Terminological reasoning, such as automatic classification of terms according to subclass (a.k.a. ‘is-a’) relations, plays one of the central role in applications of biomedical ontologies. To effectively deal with large ontologies, several profiles of the W3C standard OWL 2 have been defined [7]. Among them, the OWL EL profile aims to provide tractable terminological reasoning. Specialized OWL EL reasoners, such as CEL [1], Snorocket [5], and jCEL [6], can offer a significant performance improvement over general-purpose OWL reasoners. This paper describes the ELK system (http://elk-reasoner.googlecode.com/). ELK is developed to provide high performance reasoning support for OWL EL ontologies. The main focus of the system is (i) extensive coverage of the OWL EL features, (ii) high performance of reasoning, and (iii) easy extensibility and use. In these regards, ELK can already offer advantages over other OWL EL reasoning systems mentioned above. For example, as of today, ELK is the only system that can utilize multiple processors/cores to speed up the reasoning process, which makes it possible to classify SNOMED CT in as little as 5 seconds on a commodity hardware [2]. This paper does not provide any new theoretical results or experimental comparisons with other tools; those can be found in our earlier works [2–4]. ELK is a flexible system that can be used in a variety of configurations. This is supported by a modular program structure that is organized using the Apache Command-line Client Reasoner OWL FSS Parser Protégé Plugin OWL API Bindings OWL Object Interfaces Indexing