In this chapter we have covered most important aspects of function block type definition. We have reviewed how type definitions can then be used to create function block instances. In turn, we have seen how Function Block Instances can be used in new type definitions to hierarchically build function blocks of yet higher functionality. Although designs can be created graphically, we have noted that the standard also defines a formal textual syntax that can be used as an alternative representation.

To summarise:

• There are three categories of function block: (i) basic, (ii) composite and (iii) subapplication.

• The behaviour of a basic function block is defined in terms of an Execution Control Chart (ECC) and one or more algorithms.

• Composite function blocks are defined in terms of a network of component function blocks.

• Subapplication blocks are similar to composite function blocks but also have the flexible characteristic that they can be distributed to run on more than one resource.

• Service Interface function blocks provide a way to model the interaction between the resource and the underlying hardware and communications systems.

• All function block type definitions can either be defined graphically or textually. The graphical and textual representations are interchangeable.