We claim that a general conceptual framework for the IS field should provide some kind of common upper-level ontology to describe and explain artifact- mediated social interaction. Such an ontology, socio-instrumental pragmatism (SIP), has been suggested. Our aim is to refine and formalize this ontology by providing a meta-model in the form of a unified modeling language (UML) class diagram. We discuss the implications of such a model as well as its relation to other ontologies. The meta-model is validated by using it in the evaluation of an existing business modeling language.