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ISO/IEC 19756:2011 (TMCL) is a constraint language for Topic Maps, allowing definitions of Topic Maps schemas to be written in a precise and machine-readable form. This makes it possible to validate a topic map against a TMCL schema to see if it conforms to the constraints in the schema, and also enables other uses, such as schema-driven editors and object mappings.

TMCL is defined as a Topic Maps vocabulary consisting of a number of topic, association, occurrence, and role types, identified by Published Subject Identifiers (PSIs), and defined using English prose. It defines the concept of validation, by which a given topic map is valid according to a schema if it conforms to all the constraints in that schema and a number of global validation rules which apply to all topic maps independent of schema.

TMCL does not have any syntax of its own, since it is defined simply as a Topic Maps vocabulary. However, a number of CTM templates are defined in ISO/IEC 19756:2011 in order to facilitate authoring of TMCL schemas using CTM.