<Dd> The theory of computation classifies languages by the computations they are capable of expressing . All Turing complete languages can implement the same set of algorithms . ANSI / ISO SQL - 92 and Charity are examples of languages that are not Turing complete, yet often called programming languages . </Dd> <P> Markup languages like XML, HTML, or troff, which define structured data, are not usually considered programming languages . Programming languages may, however, share the syntax with markup languages if a computational semantics is defined . XSLT, for example, is a Turing complete XML dialect . Moreover, LaTeX, which is mostly used for structuring documents, also contains a Turing complete subset . </P> <P> The term computer language is sometimes used interchangeably with programming language . However, the usage of both terms varies among authors, including the exact scope of each . One usage describes programming languages as a subset of computer languages . In this vein, languages used in computing that have a different goal than expressing computer programs are generically designated computer languages . For instance, markup languages are sometimes referred to as computer languages to emphasize that they are not meant to be used for programming . </P> <P> Another usage regards programming languages as theoretical constructs for programming abstract machines, and computer languages as the subset thereof that runs on physical computers, which have finite hardware resources . John C. Reynolds emphasizes that formal specification languages are just as much programming languages as are the languages intended for execution . He also argues that textual and even graphical input formats that affect the behavior of a computer are programming languages, despite the fact they are commonly not Turing - complete, and remarks that ignorance of programming language concepts is the reason for many flaws in input formats . </P>

Are programming languages a subset of computer languages