A modeling language is a notation for expressing data, information or knowledge or systems in a structure that is defined by a consistent set of rules.

A modeling language can be graphical or textual. A graphical modeling language uses a diagramming technique with named symbols that represent concepts and lines that connect the symbols and represent relationships and various other graphical notation to represent constraints. A textual modeling language may use standardized keywords accompanied by parameters or natural language terms and phrases to make computer-interpretable expressions. An example of a graphical modeling language and a corresponding textual modeling language is EXPRESS.

Not all modeling languages are executable, and for those that are, the use of them doesn't necessarily mean that programmers are no longer required. On the contrary, executable modeling languages are intended to amplify the productivity of skilled programmers, so that they can address more challenging problems, such as parallel computing and distributed systems.

A large number of modeling languages appear in the literature.

Example of graphical modeling languages in the field of computer science, project management and systems engineering:

Examples of graphical modeling languages in other fields of science.

Information models can also be expressed in formalized natural languages, such as Gellish. Gellish has natural language variants such as Gellish Formal English and Gellish Formal Dutch (Gellish Formeel Nederlands), etc. Gellish Formal English is an information representation language or semantic modeling language that is defined in the Gellish English Dictionary-Taxonomy, which has the form of a Taxonomy-Ontology (similarly for Dutch). Gellish Formal English is not only suitable to express knowledge, requirements and dictionaries, taxonomies and ontologies, but also information about individual things. All that information is expressed in one language and therefore it can all be integrated, independent of the question whether it is stored in central or distributed or in federated databases. Information models in Gellish Formal English consists of collections of Gellish Formal English expressions, that use natural language terms and formalized phrases. For example, a geographic information model might consist of a number of Gellish Formal English expressions, such as:

whereas information requirements and knowledge can be expressed for example as follows: