Improving interface specifications with Comma

When you want to buy a new car, you go to the dealership. After you’ve made your choice, the dealer will draw up a contract. This contract is a formal document describing two clauses (figure 1). But does it contain all the information required to execute the deal? For example, is it clear whether the buyer needs to pay before or after pickup? And when exactly can he come get the car? Clearly, some important information is missing in this contract: it lacks information about the order in which the clauses need to be executed and it doesn’t specify when a clause will be executed (figure 2).

Software interfaces are like contracts. In our experience, the clauses are always described (eg in a header file), sometimes including their order, but their timing behaviour is rarely made explicit. During system development, proper interface definitions are essential to prevent integration issues. During later phases of the system lifecycle, continuous interface monitoring is important to avoid system failures due to component changes. For instance, a supplier might deliver an improved version of a component, but with different timing characteristics.