Drawing ICOM arrows on IDEF0 context and constraint diagrams
On a context diagram, you can draw Input, Control, Output, or Mechanism (ICOM) arrows from blank space into the single operational activity symbol on the diagram. You can draw output ICOM arrows from the operational activity symbol into blank space. The same ICOM arrow tool is used to draw all four types of lines.
1 Within an open Activity Model diagram, on the Draw toolbar, select the ICOM Arrow tool.
2 Draw the arrow from blank space to the side of the operational activity symbol into which you want the arrow to go, following the ICOM arrow rules of placement.
To show iterated activity in an IDEF0 child decomposition diagram, draw a call or output arrow exiting from a function or activity symbol, then loop back to that same box as an input or control.
You must use the Straight (orthogonal) line style to loop ICOM Arrows. To set line style, right-click a previously drawn ICOM Arrow; then click Format > Line Style > Straight (orthogonal).
3 Name the ICOM arrow; then click OK.
4 To tunnel the arrow, in the Associative Properties dialog box, select the appropriate Tunneled (Parentheses) check box.
When an arrow into a box is tunneled, it means that the data associated with the arrow does not need further understanding (or need to be modeled) on the next-level child decomposition IDEF0 diagram. The modeling software does not automatically add tunneled arrows to a child IDEF0 diagram.
5 Click OK.
The graphic below illustrates how ICOMs are used with a single function. The Operate Warehouse function takes Customer Order as an input, uses Inventory and Customer as Controls, uses Materials Management and Carrier as Mechanisms (mechanisms can be thought of as "resources"), and has outputs of Purchase Orders, Shipments, and Order Confirmations.
