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Semantics (from Ancient Greek: σημαντικός sēmantikós, "significant")^[1]^[2] is the study of meaning. It focuses on the relation between signifiers, like words, phrases, signs, and symbols, and what they stand for; their denotation. Linguistic semantics is the study of meaning that is used for understanding human expression through language. Other forms of semantics include the semantics of programming languages, formal logics, and semiotics. In international scientific vocabulary semantics is also called semasiology.

The word semantics itself denotes a range of ideas—from the popular to the highly technical. It is often used in ordinary language for denoting a problem of understanding that comes down to word selection or connotation. This problem of understanding has been the subject of many formal enquiries, over a long period of time, especially in the field of formal semantics. In linguistics, it is the study of the interpretation of signs or symbols used in agents or communities within particular circumstances and contexts.^[3] Within this view, sounds, facial expressions, body language, and proxemics have semantic (meaningful) content, and each comprises several branches of study. In written language, things like paragraph structure and punctuation bear semantic content; other forms of language bear other semantic content.^[3]

The formal study of semantics intersects with many other fields of inquiry, including lexicology, syntax, pragmatics, etymology and others. Independently, semantics is also a well-defined field in its own right, often with synthetic properties.^[4] In the philosophy of language, semantics and reference are closely connected. Further related fields include philology, communication, and semiotics. The formal study of semantics can therefore be manifold and complex.

Semantics contrasts with syntax, the study of the combinatorics of units of a language (without reference to their meaning), and pragmatics, the study of the relationships between the symbols of a language, their meaning, and the users of the language.^[5] Semantics as a field of study also has significant ties to various representational theories of meaning including truth theories of meaning, coherence theories of meaning, and correspondence theories of meaning. Each of these is related to the general philosophical study of reality and the representation of meaning.

Computer science

In computer science, the term semantics refers to the meaning of languages, as opposed to their form (syntax). According to Euzenat, semantics "provides the rules for interpreting the syntax which do not provide the meaning directly but constrains the possible interpretations of what is declared."^[6] In other words, semantics is about interpretation of an expression. Additionally, the term is applied to certain types of data structures specifically designed and used for representing information content.

Programming languages

The semantics of programming languages and other languages is an important issue and area of study in computer science. Like the syntax of a language, its semantics can be defined exactly.

For instance, the following statements use different syntaxes, but cause the same instructions to be executed:

Statement	Programming languages
`x += y`	C, C++, C#, Java, JavaScript, Perl, PHP, Python, Ruby, etc.
`x := x + y`	Ada, ALGOL, ALGOL 68, BCPL, Dylan, Eiffel, Modula-2, Oberon, OCaml, Object Pascal (Delphi), Pascal, SETL, Simula, Smalltalk, Standard ML, VHDL, etc.
`ADD x, y`	Assembly languages: Intel 8086
`LET X = X + Y`	BASIC: early
`x = x + y`	BASIC: most dialects; Fortran, MATLAB, Lua
`Set x = x + y`	Caché ObjectScript
`ADD Y TO X.`	ABAP
`ADD Y TO X GIVING X`	COBOL
`set /a x=x+y`	Batch
`(incf x y)`	Common Lisp
`/x y x add def`	PostScript

Generally these operations would all perform an arithmetical addition of 'y' to 'x' and store the result in a variable called 'x'.

Various ways have been developed to describe the semantics of programming languages formally, building on mathematical logic:^[7]

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.

Semantic models

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 the arcs denote relationships between them.

The Semantic Web refers to the extension of the World Wide Web via embedding added semantic metadata, using semantic data modelling techniques such as Resource Description Framework (RDF) and Web Ontology Language (OWL).

^ σημαντικός. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
^ The word is derived from the Ancient Greek word σημαντικός (semantikos), "related to meaning, significant", from σημαίνω semaino, "to signify, to indicate", which is from σῆμα sema, "sign, mark, token". The plural is used in analogy with words similar to physics, which was in the neuter plural in Ancient Greek and meant "things relating to nature".
^ ^a ^b Neurath, Otto; Carnap, Rudolf; Morris, Charles F. W. (Editors) (1955). International Encyclopedia of Unified Science. Chicago, IL: University of Chicago Press. {{cite book}}: |first3= has generic name (help)
^ Cruse, Alan; Meaning and Language: An introduction to Semantics and Pragmatics, Chapter 1, Oxford Textbooks in Linguistics, 2004; Kearns, Kate; Semantics, Palgrave MacMillan 2000; Cruse, D. A.; Lexical Semantics, Cambridge, MA, 1986.
^ Kitcher, Philip; Salmon, Wesley C. (1989). Scientific Explanation. Minneapolis, MN: University of Minnesota Press. p. 35.
^ Euzenat, Jerome. Ontology Matching. Springer-Verlag Berlin Heidelberg, 2007, p. 36
^ Nielson, Hanne Riis; Nielson, Flemming (1995). Semantics with Applications, A Formal Introduction (1st ed.). Chicester, England: John Wiley & Sons. ISBN 0-471-92980-8.

[1] σημαντικός. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project

[2] The word is derived from the Ancient Greek word σημαντικός (semantikos), "related to meaning, significant", from σημαίνω semaino, "to signify, to indicate", which is from σῆμα sema, "sign, mark, token". The plural is used in analogy with words similar to physics, which was in the neuter plural in Ancient Greek and meant "things relating to nature".

[Neurath1955-3] Neurath, Otto; Carnap, Rudolf; Morris, Charles F. W. (Editors) (1955). International Encyclopedia of Unified Science. Chicago, IL: University of Chicago Press. {{cite book}}: |first3= has generic name (help)

[4] Cruse, Alan; Meaning and Language: An introduction to Semantics and Pragmatics, Chapter 1, Oxford Textbooks in Linguistics, 2004; Kearns, Kate; Semantics, Palgrave MacMillan 2000; Cruse, D. A.; Lexical Semantics, Cambridge, MA, 1986.

[5] Kitcher, Philip; Salmon, Wesley C. (1989). Scientific Explanation. Minneapolis, MN: University of Minnesota Press. p. 35.

[6] Euzenat, Jerome. Ontology Matching. Springer-Verlag Berlin Heidelberg, 2007, p. 36

[7] Nielson, Hanne Riis; Nielson, Flemming (1995). Semantics with Applications, A Formal Introduction (1st ed.). Chicester, England: John Wiley & Sons. ISBN 0-471-92980-8.

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 The [[Semantic Web]] refers to the extension of the [[World Wide Web]] via embedding added semantic [[metadata]], using semantic data modelling techniques such as [[Resource Description Framework]] (RDF) and [[Web Ontology Language]] (OWL).
-==Psychology==
-In [[psychology]], ''[[semantic memory]]'' is memory for meaning&nbsp;– in other words, the aspect of memory that preserves only the ''gist'', the general significance, of remembered experience&nbsp;– while [[episodic memory]] is memory for the ephemeral details&nbsp;– the individual features, or the unique particulars of experience. The term 'episodic memory' was introduced by Tulving and Schacter in the context of 'declarative memory' which involved simple association of factual or objective information concerning its object. Word meaning is measured by the company they keep, i.e. the relationships among words themselves in a [[semantic network]]. The memories may be transferred intergenerationally or isolated in one generation due to a cultural disruption. Different generations may have different experiences at similar points in their own time-lines. This may then create a vertically heterogeneous semantic net for certain words in an otherwise homogeneous culture.<ref>Giannini, A. J.; ''Semiotic and Semantic Implications of "Authenticity"'', Psychological Reports, 106(2):611–612, 2010</ref> In a network created by people analyzing their understanding of the word (such as [[Wordnet]]) the links and decomposition structures of the network are few in number and kind, and include ''part of'', ''kind of'', and similar links. In automated [[ontologies]] the links are computed vectors without explicit meaning. Various automated technologies are being developed to compute the meaning of words: [[latent semantic indexing]] and [[support vector machines]] as well as [[natural language processing]], [[neural networks]] and [[predicate calculus]] techniques.
-[[Ideasthesia]] is a psychological phenomenon in which activation of concepts evokes sensory experiences. For example, in synesthesia, activation of a concept of a letter (e.g., that of the letter ''A'') evokes sensory-like experiences (e.g., of red color).