IDEF0 is a graphical notation used to create a functional model that displays the system structure and functions, as well as flows of information and material objects that link these functions. The IDEF0 main principles include:

context diagram;
decomposition;
dominance;
4 arrow types.

A context diagram is a top-level diagram on which the subject of the model is represented by a single box with its bounding arrows. This is called the A-0 diagram (pronounced A minus zero). The arrows on this diagram interface with functions outside the subject area to establish model focus. The A-0 diagram also sets the model scope or boundary and orientation. An example A-0 diagram is shown in Figure 1.

Figure 1. The A-0 diagram in the IDEF0 notation

Decomposition means the partitioning of a modeled function into its component functions. In hierarchical models, the description of the activity can be consistently detailed (decomposed) to the desired level. The child diagram of the decomposing activity covers the same area as its parent but with more details.

Domination. The IDEF0 boxes (if it’s not a context diagram) should be placed diagonally from the top left corner of the diagram to the bottom right corner. Boxes placed in the upper left “dominate” boxes placed lower and to the right through the control arrows that link them.

4 arrow types. There are four arrow types: Input, Output, Mechanism, Control.

Inputs include data or objects that are transformed by a function into outputs. Input arrows are associated with the left side of an IDEF0 box.

Outputs include data or objects produced by a function. Output arrows are associated with the right side of an IDEF0 box.

Mechanisms are the means used to perform a function. Mechanism arrows are associated with the bottom side of an IDEF0 box.

Controls define conditions required to produce the desired outputs. Data or objects modeled as controls may be transformed by a function, creating outputs. Control arrows are associated with the top side of an IDEF0 box.

Thus, the IDEF0 box shows the conversion of an input into an output by means of mechanisms based on control conditions. Table 1 contains description of the IDEF0 notation elements:

Element	Button	Shape	Description
Function			A function is a box. Inside the box there is its name and number. A function name shall be an active verb, a verb phrase or a verb noun.
Arrow			Arrows represent incoming and outgoing data or objects.
Text Annotation			Comment. The symbol may be used on a diagram of any notation.
Text			Comment without a connector. The symbol may be used on a diagram of any notation.
External Reference			An External reference is an element that models a place, entity, or an org unit that is outside the boundaries of the system being modeled. External references are used to define a source or receiver of the arrow that goes outside the model frame.

Table 1. IDEF0 Notation Elements

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