Analysing Syntactic Regularities in Ontologies Eleni Mikroyannidi, Nor Azlinayati Abdul Manaf, Luigi Iannone, Robert Stevens University of Manchester, United Kingdom, email:{mikroyannidi|abdulman|iannone|stevens@cs.manchester.ac.uk} Abstract. Syntactic regularities are repetitive structures of axioms in the asserted form of an ontology. The Regularity Inspector for Ontologies (RIO) is a frame- work for detecting such regularities in ontologies using cluster analysis. Detection of syntactic regularities can be used to identify parts of an ontology that have a similar syntactic structure, and could therefore provide an intuition of their con- struction. In this paper, we introduce uniformity in regularities, meaning the de- gree of diversity of regularities in an ontology. Based on this notion, we present an analysis of syntactic regularities in a variety of ontologies by applying RIO. The selected ontologies are mainly biomedical ontologies; processable BioPortal ontologies and SKOS vocabularies that represent biomedical concepts, gathered from the Web. Our analysis aims to show how syntactic regularities are formu- lated when a different knowledge representation language (OWL, SKOS) is used. The results have shown that the selected SKOS vocabularies were more uniform in terms of their syntactic regularities; smaller homogeneous clusters were found, and with few generalisations, but of high abstraction level and cluster coverage. Compared to SKOS vocabularies, BioPortal ontologies were regular, but more complex and less uniform. The analysis of syntactic regularities and uniformity of regularities can be helpful for gaining an intuition of the ontology design and its complexity. 1 Introduction Advancements in ontology engineering should lead to the adoption of more systematic methods and more advanced tools for ontology development. The construction of on- tologies has become a collaborative process that is often based on patterns of different granularity. These can be conceptual schemas, general guidelines, spreadsheets for col- lecting knowledge and populating the ontology, and so on [11,7]. The instantiation of these patterns should give rise to repeating regularities in the use of entities and ax- ioms. The recognition of regularities is important when authoring an ontology in order to understand it and to assure that it conforms to guidelines and agreed patterns. A syntactic regularity is defined as a set of axioms with reoccurring (regular) syn- tactic structure. We presented RIO in [9]; a framework for detecting such regularities. A regularity can be expressed with a generalisation, which is an axiom that allows for