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What is CTS2?

CTS2 is an Object Management Group (OMG) specification for representing, accessing and disseminating terminological content.

What is 'terminological content'

Terminological content represents a spectrum of different resources sharing a common characteristic that they play a role of grounding data to semantics. Terminological includes:

  • Code Systems - organized collections of identifiers whose purpose is to signify intent or meaning. Sometimes known as Knowledge Organization Systems (KOS), a code system may be a:
    • code set - flat lists of code / phrase pairs.
    • term list - a set of words (or tokens) each of which has a unique definition when used in a specified setting or context
    • thesaurus - a (semi-) structured set of words and phrases whose purpose is to enable the search and navigation of information
    • classification system - a set of non-overlapping categories used to organize and aggregate data for some specific purpose
    • ontology - a description of some subset of reality
  • Value Sets - selected subsets of the codes, categories or entity descriptions from one or more code systems.
  • Maps - a formal set of rules that specifies relations between two value sets, typically drawn from two different code systems.
  • Concept Domains - placeholders in models of databases, messages or other representational forms. (Need definition of DEC) here.

Use Cases

Why use CTS2?

CTS2 is intended to be used in any environment where data semantics are important.


Assigning meaning to identifiers has far ranging applicability. The more semantics applied to data, the better systems can communicate and ultimately inter-operate.

Broad Uses

  • When you need to exchange data between systems
  • When data needs to be recorded in a way preserves the meaning and intent
  • To link human-readable free text to machine-processable data

Specific Uses

  • Electronic Health Records (EHR)
  • Clinical Note annotation
  • Web Service discriptions/discovery metadata
  • ... many more

Because CTS2 is a recognized Object Management Group© (OMG) Standard, all of these things can be done in a uniform, consistent way.


It is important, also, to understand what CTS2 was not intended for. CTS2 is not:

  • A Database
  • Running Software -- it is a Specification (although there are Implementations).
  • An inventory management system

Navigation – Common Terminology Services (CTS2)

About CTS2
   CTS2 History
   Business Case
How it works
Implementing CTS2
   Business Case
   Glossary of Terms
   HL7 SFM
   CTS2 Development Framework
  Github Page
   Who is Using CTS2?
   Get Help