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IDEF0 Diagram IDEF0

IDEF0

IDEF0 is a method designed to model the decision, actions and activities of an organisation or system, for analysing and communicating the functional perspective of the system.

The IDEF0 assists the modeller 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.

In general, there is the same conservation of data rule between the functions at the higher level and the expansion of a function into a lower level diagram.

However, the IDEF0 notation allows these data conservation rules to be broken in a controlled way, but using tunnelled flows.

A tunnelled input or output flow is one which is newly introduced into the current diagram and which does not correspond to any input or output (as appropriate) in a higher level diagram. Once introduced, the data in the tunnelled input or output flow that must be conserved in child diagrams, unless they also use tunnelled inputs and/or outputs.

Tunnelled flows are indicated by semicircles drawn around whichever end (source or destination) of the flow is to be excluded from balancing checks.

IDEF0s are hierarchical. Their connectivity is:

Diagram of the hierarchical connectivity of IDEF0

IDEF0s are available in models in both the Essential and Implementation Domains.

Numbering of IDEF0

Hierarchical by function using the standard dot-decimal notation.

Symbols

An example IDEF0 diagram is:

Screenshot of an IDEF0

The symbols available in IDEF0 diagrams are:

Symbol Name Description Definition Expansion

Comment

Comment Makes a note anywhere in the diagram. Are always surrounded by * characters. None None

Split gate

Split Gate Used to divide incoming data into lower-level data items. None None

Join Gate

Join Gate Used to rejoin lower-level data items into a higher level item. None None

Boundary Point

Boundary Point A connection point for the initial transition to enter the initial state. None None

Function

Function A system function at the lowest level of detail of interest. Function
specification		 IDEF0
DFD
BD

Arrow (ICOM)

Arrow (ICOM) Represents a data flow line depicting input, control, output or mechanism depending on the directional placement relative to the Function symbol. Data definition None

Arrow (Tunnelled Input)

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. Data definition None

Arrow (Tunnelled Output)

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. Data definition None

Picture

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