As we know, the Workpackage is the smallest level of deliverable if the WBS. It cannot be broken down. A series of Activities produces/creates a deliverable or a Workpackage. It has an unique responsible: the Workpackage Manager.
In 3D WBS method, the deliverables are the Products (PBS). A series of Activity are deployed to create the Product. But we find the same Product in different Zones (ZBS). Hence, the Workpackage is at the crossing between Product and Zones.
More of that, the Workpackage has an unique responsible that belongs to the OBS. Hence, the Workpackage is at the crossing between OBS, PBS and ZBS.
In the matrix below, we can define the Workpackages. The colors reprent the Responsibles of the OBS.
By analyzing all the correpondances, the find the Workpackages (WP) below.
To summarize, we can write:
WORKPACKAGE = OBS x PBS x ZBS
To be understood that under the Workpackages there are the Activities.
In a schedule, the Workpackage are summary tasks.