The goal of this chapter is to give the reader a glimpse of the applications and problem areas that have motivated and to this day continue to inspire research in the important area of computer science known as programming language semantics.

Semantics is the study of meaning

Programming language semantics is the study of mathematical models of and methods for describing and reasoning about the behaviour of programs.

The word semantics has Greek roots and was first used in linguistics. Here, one distinguishes among syntax, the study of the structure of languages, semantics, the study of meaning, and pragmatics, the study of the use of language.

In computer science we make a similar distinction between syntax and semantics. The languages that we are interested in are programming languages in a very general sense. The ‘meaning’ of a program is its behaviour, and for this reason programming language semantics is the part of programming language theory devoted to the study of program behaviour.

Programming language semantics is concerned only with purely internal aspects of program behaviour, namely what happens within a running program. Program semantics does not claim to be able to address other aspects of program behaviour – e.g. whether or not a program is user-friendly or useful.