Simple definition of "semantics" as it is commonly used in relation to programming languages/APIs?

Question

It occurred to me today that although I've adopted and don't infrequently use the term "semantics" when referring to language elements and naming conventions, I don't have any sense of a formal definition.

My attempt to find a formal definition in the programming domain made my eyes glaze over.

I have a sense of its meaning from the contexts in which I've encountered it, and from its more common usage with respect to linguistics, and I typically use the term to refer to the meaning or expressiveness of the language element, or the fidelity of nomenclature to the intent, behaviour, or function of that which it names.

This definition, though, is my own idea. I was an Anthropology/English major and have never taken a Computer Science course. Is this taught in CS?

Is there a more accurate definition that can be boiled down to a statement or two, rather than an exhaustive and exhausting article?

Answer 1

A definition cribbed from here is The semantics of a programming language describe the relationship between the syntax and the model of computation.. This is pretty much exactly what your inferred definition was. The sticking point, and what made your eyes glaze over is precisely defining the model of computation.

There are many different formal models of computation and each leads to a different form of semantics. Operational Semantics is probably closest to the way most people informally model the semantics, having each fragment of code run through an interpreter and changing the state of an abstract routine. This approach breaks down in many models where concurrency or nondeterminism, etc., so there are other sematics better suited to these situations.

Answer 2

It's the meaning of the language elements in terms of what they formally mean in terms of computation (usually, and this is the operational semantics). This means that it expresses what a term of your language effectively does assuming an underlying kind of model that depends on which semantic we are talking about.

As you can see from wikipedia page you mainly have 3 kinds of semantics:

• operational semantics express the meaning of the language by specifying how an abstract virtual machine behaves whenever it executes a term. (eg: +: pops two elements from the stack and push the sum. This is NOT formal and it is NOT how you should really consider it, it's just to give you an idea). This is the most used one to describe semantics of "normal" programming languages. For example for Java you could have, for every possible term, a sequence of JVM instruction meant to be executed to model that term. Probably when you asked for the meaning of semantics this is the one you were looking for.
• denotational semantics is a different approach: you give for every term of the language a meaning that is represented by a mathematical function. So for previous example you would have a function f associated with + that contains what is the semantic (effective meaning) of the term
• axiomatic semantics is a way to annotate the terms of your language expressing how they alter the validity of some logical formulas you want to verify over your program. You should consider reading this just because the inference rules and axioms used are similar in how you develop this kind of semantics but it's explained in a practical way

From this decription you understand that a semantic is something well defined inside a context, and you need a specified context otherwise you couldn't give you language a formal definition of what its terms do..