In simulations of server/service systems, the behavior of a server can be affected by the characteristics of the transaction being processed. For example, a critical transaction can preempt a server. Therefore, modifications of the simulation that are intended to apply only to the characteristics of the server may have to consider characteristics of the transaction as well. If the behavior of a component is defined independently of the behavior of other components, we say that component is encapsulated. Encapsulation appears to be desirable; for example, it results in more flexible and more easily understood simulations.

The authors offer a modification of the way the server would be modeled that incorporates such things as provision for preemption in the characteristics of the server, that is, the model encapsulates the server. They then discuss simulation languages, such as May, Maisie, and SIM++, that support this modification, and argue that their modified approach would also facilitate parallel simulation. Finally, they note that object-oriented programming techniques could also support this modification.

Designers of simulation languages and simulation software should read this paper and decide for themselves whether the authors’ modified world view should be incorporated into their languages and programs.