UML is a standard modelling language that is able to specify a wide range of object-oriented concepts. Among them, we have collaborations, that serve to realise use cases, a powerful abstraction concept. The behaviour part of a collaboration is rendered using collaboration diagrams. However, the lack of formalisation compromises the precision of the specification. By using formal description techniques, such as Object-Z, we can reason about the requirements and identify ambiguities and inconsistencies earlier in the development process. In general, we can say that formalisation helps obtaining a more reliable system. Our aim is to formalise collaborations Object-Z class schemas. This is accomplished by proposing an integrated formal process.