... Data Models exist in people's heads. ... We will also review some of the various modelling languages available. ... It is important to note that the interface language's syntax is not a model. Instead, that syntax should be chosen so as to faithfully reflect the model which the language hopefully shares with user and system. ... So how do we make the model explicit? ... The Unified Modelling Language (UML) is intended for designing object-oriented systems, and modelling their environments. ...