Appendix A: IDEF0 notation

The notation used to describe the PO functionality is called IDEF0. The basic element of an IDEF0 model, as illustrated in Figure A.1, is a box containing a verb phrase (e.g., "execute project") describing the activity or transformation that takes place within the box. In IDEF0 syntax, inputs are shown as arrows entering from the left side of the box, while outputs are represented by arrows exiting from the right side of the box. Controls are displayed as arrows entering the top of the box and mechanisms are displayed as arrows entering from the bottom. Inputs, controls, outputs, and mechanisms (ICOMs) are all referred to as "concepts."

Figure A.1: IDEF0 syntax.

IDEF0 models are organized hierarchically, as shown in Figure A.2. The high-level activity as represented by the enveloping, shadow-edged box is broken down inside the box into smaller activities. The concepts entering or leaving the box at the higher level are "consumed" or "produced" by the lower-level activities. There is no need to match every lower-level concept with another at a higher level. This "tunneling" in IDEF0 terminology helps improve the readability of the diagrams by allowing for details to be shown where appropriate.

Figure A.2: IDEF0 hierarchical structure.

Complete information about the IDEF family of methods can be found at http://www.idef.com.