An approach to describing the functional requirements of an embedded communication system

An "abstract' requirements specification describes a system's externally visible behavior without making decisions about its design. Although they have important advantages, such specifications are difficult to produce for complex systems and hence are seldom seen in the real programming world. This report describes an abstract requirements specification for a complex, real-world system; the specification is intended to serve as a fully worked out example for those tasked to document the requirements of similar systems. After introducing the Navy application with which we are concerned, we demonstrate that the traditional approach of functional decomposition, where each output is expressed as a mathematical function of inputs, leads to premature design decisions. Next, we present a new approach to writing requirements documents that avoids design decisions and thus leads to an abstract specification. The new approach is compared to a similar approach used in a related project. An appendix provides an example that illustrates the formal techniques employed in the approach.