The use of an assertive specification language for real-time software development and maintenance is considered. The language is used for asserting the acts or relations inherent in the problem to be solved; this is in contrast to conventional programming languages, which are used to express the computer solution. Expressing a problem in Model consists of declaring array variables and defining their relationships through equations. This is different from conventional programming, which relates the problem in terms of computer operations. The language is supported by an automatic system which interacts with the user in soliciting missing definitions or correcting inconsistencies, and which translates the specification into a near-optimal computer solution. The main advantages of this approach are indicated. The use of Model in real-time software development and maintenance is reviewed. Differences from conventional programming are stressed through an example, which also illustrates the use of the three automatic components of the Model system.