A system type is a parameterized family of systems. The terminal identifiers are always among the parameters, though they are usually left implicit in the system name. Substituting an appropriate value for each parameter yields a particular system, also called an instance of the system type.
Partial substitution yields a subtype.
Many systems are known by various names. The names used in EDIS were chosen with the following criteria in mind. In a sense, the names used in EDIS are dummies , since they could be systematically replaced without affecting the global structure. Specifications Specifications of systems are given in several ways for two reasons. Some specifications can even be copied and pasted directly into a tool, without translation.