Idef0 Diagram
Purpose
IDEF0 is a method designed to model the decisions, actions and activities of an organisation or system, for analysing and communicating the functional perspective of the system.
Example
Here is an example IDEF0 Diagram.
Description
The IDEF0 Diagram assists the modeler in identifying what functions are performed, what is needed to perform those functions, what the current system does right, and what the current system does wrong. Its development owes much to the SADT (systems analysis and design technique) notation devised by Philips. Each diagram shows functions and the flows of data between them. Functions are shown as rectangles. The meaning of a flow is determined by which side of the rectangle it is connected to:
- Left side, the flow is an input into the function ( I )
- Top side, the flow is a control or constraint on the operation of the function ( C )
- Right side, the flow is an output from the function ( O )
- Bottom side, the flow is a mechanism or resource used by the function ( M )
Collectively, these are often termed ICOM flows.
Strengths
The primary strength of IDEF0 is that the method has proven effective in detailing the system activities for function modelling, the original structured analysis communication goal for IDEF0.
The description of the activities of a system can be easily refined into greater and greater detail until the model is as descriptive as necessary for the decision-making task at hand.
The IDEF0 Diagram is quite similar in nature to the well known and popular N-Squared Diagram for specifying inputs/outputs within the functional structure of a system. As a complimentary feature, it includes controls and mechanisms to depict additional input/output definition. It is a successful attempt to formally standardise a modelling notation to depict system infrastructure inputs and outputs.
Weaknesses
One problem with IDEF0 is the tendency of IDEF0 models to be interpreted as representing a sequence of activities. Without intent, activity sequencing can be embedded in the IDEF0 model.
Recommended Uses
Where detailed interface analyses are performed and results must be communicated to a large project team. The IDEF0 symbology and rules force and enforce rigor and precision into the input/output definition process.
Characteristics
APPEARS IN MODELS |
Essential and Implementation |
NUMBERING |
Hierarchical by Function |
HIERARCHICAL |
Yes |
Linkage
Symbols
 |
Comment |
Makes a note anywhere in the diagram. Always surrounded by * characters. |
None |
None |
 |
Split gate |
Used to divide incoming data into lower-level data items. |
None |
None |
 |
Join gate |
Used to rejoin lower-level data items into a higher level item. |
None |
None |
 |
Boundary point |
A connection point for the initial transition to enter the initial state. |
None |
None |
 |
Function |
A system function at the lowest level of detail of interest. |
PSpec |
IDEF0
DFD
BD |
 |
Picture |
Allows you to choose the location of a GIF or JPEG image to be displayed as a diagram symbol or to be embedded in an existing diagram symbol. |
None |
None |
 |
Arrow (ICOM) |
Represents a data flow line depicting input, control, output or mechanism depending on the directional placement relative to the Function symbol |
DD Entry |
None |
 |
Arrow (tunnelled input) |
Input information at a specific level of decomposition that is not required for understanding at some other levels. The arrow can be tunnelled at any chosen level. |
DD Entry |
None |
 |
Arrow (tunnelled output) |
Output information at a specific level of decomposition that is not required for understanding at some other levels. The arrow can be tunnelled at any chosen level. |
DD Entry |
None |
|
