Although both look very similar, there is an important difference between the frame and the block diagram. The frame does consist of slots and signals connecting them. In the slots only the inputs and outputs are defined, furthermore the type of element can be predefined, this means you can specify here which type of element shall fit into the slot (e.g. ElmVco* or ElmSym*). The frame is the basis of a composite model, where elements can be inserted into the slots.

The block diagram doesn’t have any slots but can be made up using different blocks or equations, where each block will define a function. The input/output parameters of the block diagram have to match those defined in the associated slot. Also the parameter names of the function have to match the I/O names used in the function block. The block diagram is the basis of a DSL element (ElmDsl), which can be inserted into the slots of a composite model. For more information about these topics refer to the User Manual and DSL Tutorial.