WHEN DO DIAGRAMS MAKE GOOD COMPUTER LANGUAGES

It is obvious that some diagrammatic notations are better than others, less obvious why. We list some requirements for a good notation with examples and empirical findings. Central requirements are to give the user the useful information (relevance) using a clear perceptual code for the underlying processes (representation); moreover the notation should restrict the writer to “good” structures. Important information in symbolic codes should be redundantly recoded in a perceptual code as well. Unfortunately these principles, especially the last, tend to make extra work if the diagram has to be modified, conflicting with the requirement of revisability unless software aids can be devised. Notation designers cannot turn to behavioural science for detailed guidance, but they could well make more use of empirical evaluations than at present. © 1979, Academic Press Inc. (London) Limited. All rights reserved.