The semantic rules of the language tell us how to build meaningful expressions, statements, and programs. For example, they might tell us that before using the variable request in the if-statement, we must declare that variable. They also tell us that, the declaration of a variable such as request causes storage to be reserved for the variable. It defines the meaning of syntactically correct programs in that language.
The operational approach to describing the semantics of programming languages describes the behavior of a simple and intuitive abstract processor used to describe the effects of each language construct.
To describe the operational semantics of programming languages, we introduce a simple abstract processor, called SIMPLESEM, and we show how language constructs can be executed by sequences of operations of the abstract processor.