"A process model describes the software activities in a generic sense, that is, for many different projects. It describes the process, the artifacts produced and used, and the actors responsible for the activities. A process model is a graph; it can have cycles and so on. A work breakdown structure is a tree that expands the process model’s activities with details and necessary subtasks that are specific for a particular project. A WBS task that appears in every project should also be in the process model."
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