The Document Style Semantics and Specification Language (DSSSL) was developed by ISO as a language for transforming and formatting both printed and electronic SGML-encoded documents. DSSSL defines four languages (i.e. transformation language, style language, expression language and query language) for changing, formatting and transforming SGML documents. All the four languages are declarative and are not intended to be complete programming languages, although they contain programming features, for example boolean or conditional expressions.

• The transformation language is used to transform an SGML document to another SGML-based representation (represented by zero or more SGML documents), according to a given DTD. The result of the transformation process can be used as an input of a formatting process.
• The style language allows users to specify the types of formatting to be applied on various objects during composition, layout, and pagination. It supports a wide range of typographic features. The standardization of formatting semantics is provided by a set of basic structures known as flow objects, and an associated set of formatting characteristics applied on those objects
• The expression language is the basis of all other three DSSSL languages and is a programming language with a SCHEME-like syntax. Unlike a full SCHEME, it does not have any side-effect.
• The core query language (Standard Document Query Language, SDQL) is a part of both the transformation language and the style language. It is used to navigate in the tree-like structure of SGML-encoded documents, and to get a path to the relevant parts in a transformation process.