Action semantics is a framework for the formal specification

Formal specification

In computer science, a formal specification is a mathematical description of software or hardware that may be used to develop an implementation. It describes what the system should do, not how the system should do it...

 of semantics of programming languages

Formal semantics of programming languages

In programming language theory, semantics is the field concerned with the rigorous mathematical study of the meaning of programming languages and models of computation...

 invented by David Watt and Peter D. Mosses. It is a mixture of denotational

Denotational semantics

In computer science, denotational semantics is an approach to formalizing the meanings of programming languages by constructing mathematical objects which describe the meanings of expressions from the languages...

, operational

Operational semantics

In computer science, operational semantics is a way to give meaning to computer programs in a mathematically rigorous way. Operational semantics are classified into two categories: structural operational semantics formally describe how the individual steps of a computation take place in a...

 and algebraic semantics

Algebraic semantics

An programming language theory, the algebraic semantics of a programming language is a form of axiomatic semantics based on algebraic laws for describing and reasoning about program semantics in a formal manner....

.

Action Semantics aims to be pragmatic. Action-Semantic Descriptions (ASDs) are designed to scale up to handle realistic programming languages. This is aided by the extensibility and modifiability of ASDs. This helps to ensure that extensions and changes do not require too many changes in the description. This is in contrast to the typical case when extending denotational or operational semantics, which may require reformulation of the entire description.

The Action Semantics framework was originally developed at the University of Aarhus

University of Aarhus

Aarhus University , located in the city of Aarhus, Denmark, is Denmark's second oldest and second largest university...

 and the University of Glasgow

University of Glasgow

The University of Glasgow is the fourth-oldest university in the English-speaking world and one of Scotland's four ancient universities. Located in Glasgow, the university was founded in 1451 and is presently one of seventeen British higher education institutions ranked amongst the top 100 of the...

. Groups and individuals around the world have since contributed further to the approach.