Visualising action contracts in object-oriented modelling

In recent years a number of OO methods have been enhanced with textual, mathematical languages for specifying invariants and action contracts (pre and post conditions). This paper builds on a recent proposal for ‘constraint diagrams’, a diagrammatic notation allowing the expression of such assertions. Constraint diagrams essentially provide a pictorial representation of navigation expressions, specifically the sets of objects they define, and, using Venn diagrams and other techniques, constraints on the cardinalities of and relationships between those sets. The original proposal focused on the use of constraint diagrams for depicting invariants. This paper focuses on their use in depicting action contracts.