Output and Diagram Essays

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READING & CRITIQUING AN IDEF0 MODEL by William D. Waltman Adrien Presley

Enterprise Integration Frameworks Group Automation & Robotics Research Institute
7300 Jack Newell Blvd. Fort Worth, Texas 76118 (817) 794-5900

July 1993

IDEF0 is a modeling tool used to produce a model or structured representation of the functions of a system and of the information and objects which tie those functions together. A system can be any combination of hardware, software, and people. An IDEF0 model consists of diagrams and text pages describing the diagrams. Diagrams are the major components of a model and this document will concentrate on how to read them. IDEF0 methodology recognizes that successful systems development requires input and validation from the people who will ultimately use the system. The Author/Reader Cycle serves as the mechanism to facilitate communication between systems analysts and users. This is accomplished by distributing Kits containing IDEF0 models and supporting documentation to the Reader community for comment. When the Kits have been read and critiqued, they are returned to the Author. This cycle may go on for many iterations.

The overall purpose of this paper is to provide new Readers with a brief overview of how to read IDEF0 models and to constructively comment. We first discuss some of the basic syntax necessary to read an IDEF0 model. Next, the makeup of Kits, which act as the vehicle for information exchange between Author and Reader, are discussed. Finally, The Author/Reader cycle is discussed, with emphasis on the responsibilities of the Reader. APPENDIX A provides a definition of words printed in Bold throughout the paper.

Functions are represented by boxes and interfaces are represented by arrows, depicted in Figure 1a.
Blueprint "CONTROL" "INPUT" "FUNCTION" "OUTPUT" Raw Materials Make Part Scrap "MECHANISM" Tools Machines Fabricated Part Work Order Schedule

Figure 1a

Figure 1b

The boxes represent functions such as activities, actions, processes or operations. Boxes are denoted by an active verb phrase inside the box, such as the "Make Part" box in Figure 1b.


Arrows indicate data. In IDEF, data can be information (like "current status") or physical objects (like "raw materials"). They are named by noun phrases such as "Raw Materials" or "Tools". The position of the arrow indicates the type of information being conveyed. The arrows entering and leaving the boxes on the left and right represent "Inputs" and "Outputs", respectively. Inputs represent data needed to perform the function. Outputs show the data that is produced as a result of the function. The function transforms the inputs into the outputs. Arrows which enter from the top indicate "Controls", or things which constrain or govern the function. Arrows entering the bottom of the boxes are "Mechanisms". Mechanisms can be thought of as the person or device which performs the function.


More General
1 2 3 4 A0

1 2 3 A2

This diagram is the "parent" of . . . this diagram.

More Detailed
1 2 3 A23

Figure 2: Decomposition Overview An IDEF model is made up of several diagrams. Each diagram describes in more detail a box from a more general diagram. The process of describing a box in more detail is known as decomposing a function. The more general diagram is called the parent of the detailed diagram. IDEF models are read in a "Top-Down" fashion. The top level diagram, also called the Context or A-0 Diagram, summarizes the overall function of the system which is represented by a single box. The A0 diagram represents the first decomposition of the system. The A0 and all subsequent diagrams must contain 3 to 6 2

numbered boxes. The numbers help tie the diagrams together. For example, in Figure 2, Box 2 of the A0 is decomposed on diagram A2. Box 3 of A2 is decomposed on diagram A23 and so forth. All diagrams are named beginning with the