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WBS is nothing but Work Breakdown Structure. It is mainly used in Project System (PS) module. Tcode: CJ20N. For any project defined we must have atleast one WBS. Within this WBS we can have networks. Networks are nothing but the series of activities. Material are used to perform the activities.
A work breakdown structure, or WBS, is a model that can be used for this purpose. In this model you devide the workload in the named phases and appoint the needed area's, tasks and activities under thes phases.