The PERA model indicates that Control and Information System products (both hardware and software) may be related to

1. the physical plant (via the Enterprise Architecture Diagram), or
2. to the Human and Organizational part of the enterprise (via the Organization Chart).

Either way may be used, however, in most cases one works better than the other. As a general rule, software is best organized by user group (Org Chart), and Hardware is best associated with Physical Plant (Architecture Diagram).

There are exceptions however. For example, a DCS (Distributed Control System) or Supervisory Optimization System consists of both hardware and software, but in this case, both are best associated with a plant area. Conversely, in a non-industrial environment, such as an engineering design office, where there are a large number of people, but little specialized hardware, it may make more sense to associate both hardware and software with the user group (by Org Chart).

It is also possible to associate software and hardware, with Supply Chain Management Diagrams and Work Flow Diagrams, or with vendors, or general industry divisions (like continuous process industries and discrete manufacturing industries), or many other ways too numerous to list. We believe, however, that these ways of organizing hardware and software product information are less likely to stand the test of time, than the simple expedient of relating products to either the physical plant, or the people, as indicated by the PERA diagram.