Systemic-Functional Linguistics (SFL) is a theory of language that focuses on the functional purpose of language in social contexts. Developed by Michael Halliday and others, SFL centers around the notion that language function is central to understanding language structure. The theory consists of four strata: Context, Semantics, Lexico-Grammar, and Phonology-Graphology. Each stratum is further divided into sub-components, such as ideational semantics, interpersonal semantics, and textual semantics.SFL also emphasizes the use of "system networks" to represent the choices present in making an utterance. These choices are called "features," which are constrained by those on other strata. For example, the decision to use a nominal group rather than a clause is determined by both the textual structure of the entire text and the social context.SFL has been influential in areas such as language education, natural language processing, and child language development. The theory has also evolved over time, with new generations of researchers contributing to its development. Today, SFL is taught around the world, and has influenced numerous computational linguistics systems, including those used in natural language generation.References:Halliday, M.A.K. (1961). Categories of the theory of grammar. Word, 17(3), reprinted in Bertil Malmberg (ed.),... Abridged version in Halliday (1976).Halliday, M.A.K. (1994). Introduction to Functional Grammar, Second Edition, London: Edward Arnold.Martin, J.R. (1992). English Text: System and Structure, Amsterdam: Benjamins.