The chapter reviews and augments a previously proposed template for defining enterprise and information systems (IS) modelling constructs. The purpose of the template is to provide clear and precise definitions of modelling constructs in a common format and, thereby, to facilitate intra- and inter-language integration. The template is based on the Bunge-Wand-Weber (BWW) model of information systems and has been used on several existing modelling languages and frameworks. It is defined by a meta-model expressed as a UML class diagram. The purpose of this chapter is to clarify the template further by formalising the meta-model through semi-formal constraints expressed in the object constraint language (OCL) and by populating the meta-model with definitions of example constructs from the UML version 1.4. The purpose is to make the template easier to understand, to validate it, to pave the way for stronger tool support for the template and to further our work on providing a complete template-based definition of the UML.