Formal syntax and semantics of basic function blocks in IEC 61499

The use IEC 61499 (International Electrotechnical Commission, IEC) as a modelling language for distributed industrial process measurement control systems lacks formal syntax and explicit semantics and can hardly ensure reliability and validity of systems. As the basic modelling elements in IEC 61499, syntax and semantics of basic function block (BFB) are specified informally and ambiguously. Hence, the formal syntax and explicit semantics of BFB are advanced to achieve the behavioural consistency and correct results, in this article. The formal syntax is defined by mathematical set theory and the explicit semantics are composed of two kinds of semantics: denotational and execution semantics. The denotational semantics explain the meaning of language with an extended Mealy finite-state machines for the formal verification in a formal way. The execution semantics provide execution rule and algorithm scheduling in the execution process and involve an input machine and the main part, in which input machine masters the matching relation of event and data input variables and the main part offers execution orders and algorithm computation. Besides, the execution semantics of BFB are exemplified with two events and algorithms as the execution order t(1)-t(20), and a flowchart of BFB behaviours is given as an overview of the processing steps for implementation or code generation.