Design patterns have been used successfully in recent years in the software engineering community in order to share knowledge about the
structural and behavioural properties of software. There is a growing body of research in the area of design pattern detection and design recovery,
requiring a formal description of patterns which can be matched by tools against the software that is to be analysed. We propose a novel approach to the formal definition of design patterns that is based on the idea that design patterns are knowledge that is shared across a community and that is by nature distributed and inconsistent. By using the web ontology language (OWL) we are able to formally define design patterns and some related concepts such as pattern participant, pattern refinement, and pattern instance.We discuss the respective ontology and give examples of how patterns can be defined using this ontology.We present the prototype of a Java client that accesses the pattern definitions and detects patterns in Java software, and analyse some scan results. This leads to the discussion on design pattern instantiation.