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math :: theory of computation :: terms
Semantics (from Ancient Greek: σημαντικός sēmantikós, "significant") is the study of meaning, reference, or truth. The term can be used to refer to subfields of several distinct disciplines including mathematical logic, linguistics, philosophy, and computer science.
In linguistics, semantics is the subfield that studies meaning. Semantics can address meaning at the levels of words, phrases, sentences, or larger units of discourse. One of the crucial questions which unites different approaches to linguistic semantics is that of the relationship between form and meaning.
In modern philosophy, the term "semantics" is often used to refer to linguistic formal semantics, which bridges both linguistics and philosophy. There is also an active tradition of metasemantics which studies the foundations of natural language semantics.
In CS, the term "semantics" refers to the meaning of language constructs, as opposed to their form, which is the domain of syntax. Semantics provides the rules for interpreting the syntax which do not provide the meaning directly but constrains the possible interpretations of what is declared.
The semantics of PLs is an important area of study in CS. Like the syntax of a language, its semantics can be defined exactly.
PLs use different syntax to describe things, which nevertheless amount to the same (the statements have the same meaning). For example, syntax for addition uses different statement across many PLs but means the same in each one.
The 3 major ways to describe the semantics of a PL formally, by building on mathematical logic are:
Operational semantics: The meaning of a construct is specified by the computation it induces when it is executed on a machine. In particular, it is of interest how the effect of a computation is produced.
Denotational semantics: Meanings are modelled by mathematical objects that represent the effect of executing the constructs. Thus only the effect is of interest, not how it is obtained.
Axiomatic semantics: Specific properties of the effect of executing the constructs are expressed as assertions. Thus there may be aspects of the executions that are ignored.
The Semantic Web refers to the extension of the World Wide Web via embedding added semantic metadata, using semantic data modeling techniques such as Resource Description Framework (RDF) and Web Ontology Language (OWL).
On the Semantic Web, terms such as semantic network and semantic data model are used to describe particular types of data model characterized by the use of directed graphs in which the vertices denote concepts or entities in the world and their properties, and the arcs denote relationships between them.
These can formally be described as description logic concepts and roles, which correspond to OWL classes and properties.
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