3.3. The BDD Frame
The diagram kind abbreviation for a block definition diagram is bdd. The model element type that the diagram frame represents can be any of the following:
As discussed in Section 2.4, “General Diagram Concepts,” the model element that the diagram represents serves as the namespace for the other elements shown on the diagram. A namespace is simply a model element that’s allowed to contain other model elements; that is, it can have other elements nested under it within the model hierarchy. A namespace, therefore, is a concept that has meaning only within your system model; it has no meaning within an instance of your system.
Many kinds of SysML elements can serve as namespaces. A package, however, is the most common kind of namespace for the various elements of definition that appear on BDDs. Therefore, the element that’s named in the header of a BDD typically is a package you’ve created somewhere in the model hierarchy.
The name of the BDD in Figure 3.1 is “DellSat-77 Satellite Structure and Properties.” The diagram header also tells us that this diagram represents the Structure package in the system model. The Structure package, therefore, is the namespace for the elements shown on the diagram.
Figure 3.1 A sample block definition diagram (BDD)
Let’s take a look in detail at the kinds of elements and relationships you can display on a BDD.