Tunneling is an IDEF0 technique for hiding input/output flows between activity diagrams levels. Sometimes input/output flows at one level are not relevant at a lower level. Usually this is because either the input/output flows are obvious or they provide unnecessary detail at that lower level and they will be revealed later in the model.

A tunnel is an arrow (with special notation) that does not follow the normal requirement that each arrow on a diagram must correspond to arrows on related parent and child. A tunneled arrow is used to provide information at a specific level of decomposition that is not required for understanding at some other levels. An arrow can be tunneled at any chosen level. Tunneling an arrow at the unconnected end means that the data or objects are not necessary at the next higher (parent) level and hence shall not be shown connecting to the parent box.

Tunneled flows are indicated by a parenthesis at the arrow head start of the input tunnel (Task Orders as a tunneled input to Plan Mission)

and from the tail of where the tunneled flow eventually emerges as an input to a lower activity.

The rule adopted is that each tunneled input/output flows must be unique within an Activity model. This ensures that the correct set of Information Exchanges will always be produced. Thus, the example below is valid and the correct Information Exchange will be formed for Mission Reports between Plan Mission and Prepare Task Plan.

However, the following example is not valid and must be avoided.