Principles of System Design with Nets

Taking the organization of a library as an example, let us begin with the most basic meaningful structure of a library. The users of the library have access to a stock of books kept in the stacks. Thus, we are dealing here with two components. It would seem obvious enough to describe one of the components (the stock of books) as being passive, and the other (the users) as being active. If we represent the passive component with a circle and the active component with a box we have the configuration shown in Fig. 1. The arrows between the components indicate the flow of objects and information.