Leaf activities are those lowest activities in an activity model that are not decomposed any further. Activity models are decomposed down to the appropriate level for the purposes of the architecture.

Usually, this would be to the level (leaf node activities) where an activity is capable of being associated with an operational node or to where an activity can be assigned to an individual role (person) or system. These are judgment calls and likely to be iterative as the architecture is refined.

Information Exchanges and Needlines are formed from leaf activities, their input/output information flows, and their node associations. It is only when Needlines are associated with Information Exchanges formed from leaf activities, that a correct and valid OV-2 Operational Node Connectivity diagram and OV-3 Operational Information Exchange Matrix can be obtained.

Information exchanges are formed by first associating Activity with Nodes (and optionally Roles). A matrix editor has been defined specifically for this purpose.

Information exchanges need to be also formed by associating External Activities with External Nodes. A matrix editor has been defined specifically for this purpose.