Internal block diagram
The SysML Internal Block Diagram (IBD) allows the designer to refine the structural aspect of the model. The IBD is the equivalent of the composite structure in UML. In the IBD properties (or parts) are assembled to define how they collaborate to realize the behavior of the block. A part represents the usage of another other block.
The most important aspect of the IBD is that it allows the designer to refine the definition of the interaction between the usages of blocks by defining Ports, as explained below.
Ports
Ports are parts available for connection from the outside of the owing block. Ports are typed by interfaces or blocks that define what can be exchanged through them. Ports are connected using connectors that represent the use of an association in the IBD.
Two types of ports are available in SysML: Standard ports handle the requests and invocations of services (function calls) with other blocks, and flow ports let blocks exchange flows of information or material.
For standard ports, an interface class is used to list the services offered by the block. For flow ports, a Flow Specification is created to list the type of data that
can flow through the port. When only a single type of object can flow through a
port, then the type is used as type for the port directly. Such a port is named Atomic Port. The class Item Flow is used to represent what does actually flow
between blocks in a particular usage context. We refer the interested reader to the standard specification for more details on item flows.6 The IBD is shown in Figure
6SysML 1.0 Specification
