Prototype theories are an important family of cognitive theories of concepts that model the classification under a concept in terms of the proximity of an object to the prototype of the concept. While logic-based definitions of concepts are standard in Description Logics and OWL, prototype-based definitions are not directly available, although they are very useful whenever we need to model commonsense concepts or data dependent classifications. We propose a strategy to define prototypes in OWL enriched with SWRL (SemanticWeb Rule Language). By means of data properties we model the weighted features of prototypes, and, by using SWRL constraints, we implement the computation of the proximity of an instance to a prototype. We also leverage a foundational ontology to provide semantics of the features occurring in prototype descriptions. We exemplify our treatment in Protégé.