Reasonable Ontology Templates: APIs for OWL Efficient and Practical Ontology Design and Maintenance Martin G. Skjæveland 1 , Henrik Forssell 1 , Johan W. Klüwer 2 , Daniel Lupp 1 , Evgenij Thorstensen 1 , and Arild Waaler 1 1 Department of Informatics, University of Oslo 2 DNV GL, Norway Abstract. Reasonable Ontology Templates, OTTRs for short, are OWL ontology macros capable of representing ontology design patterns (ODPs) and closely integrating their use into ontology engineering. An OTTR is itself an OWL ontology or RDF graph, annotated with a special purpose OWL vocabulary. This allows OTTRs to be edited, debugged, published, identified, instantiated, combined, used as queries and bulk transformations, and maintained—all leveraging existing W3C standards, best practices and tools. We show how such templates can drive a technical framework and tools for a practical, efficient and transparent use of ontology design patterns in ontology design and instantiation. 1 Introduction Ontology-based methods have matured to where they offer knowledge workers practical solutions for data management. In particular, tools that support W3C recommendations, such as reasoning tools for OWL ontologies, are sufficiently stable and efficient to allow wide-scale industrial use. However, from the perspective of product vendors and consultancy companies in the IT industry, ontologies are still viewed as a fringe technology. Hence ontology-based solutions are rarely proposed to enterprise customers, and support from the software industry is limited. One factor that impedes uptake is the high cost of establishing and maintaining a high-quality ontology. In part this is due to the scarcity of ontology experts, with availability in most cases below critical mass, and the lack of abstraction mechanisms and tool supported methods for applying ontology design patterns ODPs[2] in ontology engineering. Efficient tool support is imperative to industrial scale deployment of ontology-based methods. The work reported on in this paper has the potential to remedy the situation; Rea- sonable Ontology Templates (OTTRs) [6, An extended version of the current paper] are simple, but powerful, templates or macros for ontologies, cf. [7], represented in OWL using a dedicated OWL vocabulary. An OTTR can be viewed as a parameterised ontology which can be nested, i.e., defined using other OTTRs, and instantiated by providing arguments to fit the parameters of the template. By recursively expanding an OTTR by replacing any contained OTTR with the pattern it represents, we obtain a (regular) OWL ontology. Using this feature, we can reason both on the OTTR specification and its expansion, and additionally leverage existing W3C languages and tools for different ontology engineering tasks—all driven by OTTRs. Specifically, the implicit mapping between an OTTR’s parameters and its pattern may be exploited to generate various