The internal block diagram (IBD) has a close relationship to the BDD. You can display various elements on an IBD to express aspects of a system’s structure that complement the aspects conveyed on BDDs. IBDs also have unique capabilities that make them an essential addition to your modeling toolbox.
You create an IBD to specify the internal structure of a single block. Like a BDD, an IBD is a static (structural) view of the system or one of its parts. Unlike a BDD, an IBD does not display blocks; it displays usages of blocks—that is, the part properties and reference properties of the block that is named in the header of the IBD.