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CTS stands for Common Terminology Services. This project represents an effort to build and standardize the second release of CTS, hence CTS2.

This page is merely a high level overview and is not the primary documentation for this effort. Here we discuss the purpose, scope, and timeline of the project. In the links section at the bottom you will find pointers to the CTS2 home page.

CTS2 Service Description and Purpose

The goal of the Common Terminology Services 2 (CTS2) Specification is to expand the original functionality outlined in HL7's Common Terminology Service (CTS) Specification. CTS2 defines the functional requirements of a set of service interfaces to allow the representation, access, and maintenance of terminology content either locally, or across a federation of terminology service nodes.

The CTS2 specification strives to expand on the original functionality outlined in HL7's Common Terminology Service specification, specifically looking to:

  1. Establish the minimal common structural model for terminology behavior independent from any specific terminology implementation or interchange model, and how it is related to meta-data (information about data) and data (the information itself)
  2. Integrate into CTS2 the functional coverage outlined in the existing CTS specification.
  3. Specify both an information and functional model that addresses the relationships and use of terminology, e.g. how value sets are built and queried, and how terminological information is validated.
  4. Specify the interactions between terminology providers and consumers - how terminology users can submit unambiguous requests for corrections and extensions and how revisions to content are identified, distributed and integrated into running systems.
  5. Specify how mapping between compatible terminologies and data models is defined, exchanged and revised.
  6. Specify how logic-based terminologies can be queried about subsumption and inferred relationships.
  7. Engage broad community participation to describe the dimensions of use and purpose for vocabularies and value sets. This aim will attempt to harmonize these efforts in terms of models, use cases, and requirements for creating a functional model for CTS2.


To address the above stated purpose of CTS2, the scope of functionality addresses several broad categories.

Terminology services represent functions necessary to manage, search, and access terminology content. Terminology services provide a consistent specification for accessing and managing terminology content, independent of the terminology content and underlying technology stack. Terminology content represents various resources including lists, value sets, taxonomies, and formal description logic based ontologies. The following thematic areas are considered in scope for CTS2.

  • Administration: This is a set of functionality that provides the ability to manage content as part of a terminology service. Administration functions include the ability to load terminologies, export terminologies, activate terminologies, and retire terminologies. These functions are generally protected and accessible by service administrators with appropriate authorization.
  • Search / Query: This is a set of functionality that provides the ability to find concepts based on some search criteria. This includes restrictions to specific associations or other attributes of the terminology, including navigation of associations for result sets. This represents the primary utility for using terminology content in a number of application contexts.
  • Authoring / Maintenance: This is a set of functionality that provides the ability to create and maintain content. From a terminology service perspective, this would include the appropriate APIs to add, change, or delete concepts and associations. This would also include the processing of change events from various terminology providers.
  • Associations: This is a set of functionality that provides the ability to map concepts and the concept's associated attributes from a source terminology to a concept in a target terminology, or create relationships between concepts within a single code system.

CTS2 is intended to allow the look up and management of a wide variety of terminology components, including, but not limited to, Concepts, Associations, and Value Sets. This includes the ability to resolve content bound to a specific Context of Use (Concept Domain) or Jurisdictional Domain (Realm). At the functional level, the service interface will explicitly allow the query, definition, publication, and modification of the different terminology components that are required of terminologies and terminology services.

Conformance profiles are defined in this specification which are intended to focus specific implementations of CTS2 to address a specific class of functionality and pre-define minimum trait sets for each specified functional class. This will also allow for performance optimizations to be defined for terminology searches and queries (which are implementation considerations which will be considered in the technical specification arising from the OMG RFP process) The scope of this functional specification covers support for multiple terminology sources and a federated terminology environment.

Participation and Progress

Complete OMG Timeline

The following timeline is a modification of the original, with two additional meeting cycles added to allow additional work and harmonization of the specification.

OMG Timeline

Event or Activity

Actual Date

RFP placed on OMG document server


Preparation of RFP by TF


Approval of RFP by Architecture Board
Review by TC


TC votes to issue RFP


LOI to submit to RFP due


Voter registration closes


Initial Submissions due and placed on OMG document server ("Four week rule")


Initial Submission presentations


Update to Health Care and Ontology PSIG group


Update HL7 Vocabulary and SOA Working Group


Update OMG Healthcare and Ontology PSIG Group


Revised Submission due and placed on OMG document server ("Four week rule")


Revised Submission presentation

2011/06/20 - 2011/06/24

Final evaluation and selection by TF / Recommendation to AB and TC

2011/06/20, 2011/06/23

TC votes to recommend specification


Approval of recommendation by Architecture Board / Review by TC


Platform Technical Committee Adoption Vote / Charter Finalization Task Force


Publication of Beta Specification to OMG website


Finalization Task Force Report to AB

2012/06/18 - 2012/06/22

BoD Vote to adopt specification

2012/09/10 - 2012/09/14

LexEVS 6.0 Preliminary CTS2 Functionality Implementation Overview

Common Terminology Services - Release 2

  • Common Terminology Services release 2 (CT 2) specifies a set of service interfaces that standardize necessary functional operations of a terminology service.

    As a reference implementation, LexEVS 6.0 will provide expanded support for value sets, develop the ability to provide local extensions to code sets, provide expanded mapping ability among code sets and develop other capabilities called for in the CTS2 specification.

  • LexEVS 6.0 will add comprehensive support for CTS2 functionality that are either partially supported or unsupported in LexEVS 5.1.
  • CTS2 functionality is available for local, distributed and analytical grid services.
  • CTS2 service interfaces are exposed by the local runtime API.

diagram of LexEVS 6.0 architecture

LexEVS 6.0 CTS2 Functionality Enhancements

  • Content Dependency Notification
  • Code System Authoring/Curation
  • Value Set Authoring/Curation
  • Concept Domain Authoring/Curation
  • Usage Context Authoring/Curation
  • Association Administrative Functionality
  • Association Search/Query Functionality
  • Association Author/Curation Functionality
  • Value Set and Concept Domain Search/Query