1 Teaching Computer Applications How To Understand Each Other. Wim Gielingh TNO-IBBC P.O.Box 49, 2600 AA Delft, The Netherlands The goal of the future standard STEP is to exchange product model data between advanced CIM software-applications, which allows these applications to interpret the meaning of the exchanged data without human intervention. This requires the development of a 'language' for communication between CIM-components that supports the exchange of messages without loss of semantic content. Product models based on (form) features may provide some meaning for advanced CIM applications, but this approach appears to be insufficient for the exchange of complex messages. An outline of such a 'language' for communication between CIM-applications is given by defining first of all three distinct modelling spaces: product definition, representation and presentation. Implicit and explicit product representations are placed in these modelling spaces. A more detailed distinction is made between product definition (including shape aspects), idealization and representation. An example is given of the application of an idealization and representation independent kind of topology (Meta-topology) and its mapping on topological entities for different idealizations and representations. This approach may be of importance for the mapping of different views of the product on a semantic level, when software for the automatic recognition of (form) features has to be applied. Communication, art or science? Nobody knows precisely when and how it happened, but a long time ago man learned to communicate. It must have been a gradual, slow process of learning how to exchange and interpret messages. Mankind developed an information infra-structure. The rules for this information infra-structure are not strongly based on standards, but more on evolution and temporary agreements. Natural languages for communication are subject to evolution: the meaning of a word changes in time. Also local, regional differences exist which make it difficult to communicate with others. Natural languages reflect also areas of expertise: a lawyer uses an other language when he does his job than a pitch-man. The pitch-man would be less successful if he used the language of a lawyer when he tries to sell his products. A language can be used for communication in many different ways. Natural languages were originally spoken, allowing only direct communication with people nearby. Languages became more powerful when they were written: thoughts and ideas could even survive the sender of