We now look at some of the more general principles which should be applied when creating an information model. These principles have evolved through experience in creating a wide variety of models. We have tried to separate the topics but, as with any non-trivial subject, there are inevitably overlaps between these, and also some of the principles exhibit a creative tension between them. That is to say that complete adherence to one principle may prevent complete adherence to another; there are trade-offs that can be made and these will vary according to the modeling scope and purpose, and the choice of representation methods. In general, an information model should be precise, complete, non-ambiguous, minimally redundant and implementation independent. The modeling should tend towards clarity rather than conciseness. An information model, although if defined via EXPRESS is computer interpretable, should primarily be designed for a human reader. The modeling constructs should be chosen to aid the reader rather than obfuscate understanding by using complex, intertwined or opaque definitional relationships, particularly if they are comingled with obscure, pretentious, tautological and circumlocutory prosody. It is advantageous to present a model in more than one way, for example using both lexical and graphical representations. This, though, raises a potential ambiguity problem when the multiple representations are not in agreement. Any model that involves multiple representations must be clear about which representation is primary, so the ‘legal’ source is clear in case of disagreements between the various model forms. Define the scope and assumptions of the information model. This should be done at the start of the modeling project. It may turn out that for a complex model, the overall scoping statement can be partitioned into several more detailed scopes each of which serves a particular purpose in the overall model. A scope also defines a context in which the model items reside, thus providing a specific viewpoint in which the items are defined. One view of a model is that it can be considered to consist of a set of scopes and contexts within which the details are represented. The model should be documented according to these aspects.
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