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NLM Launches VSAC Intensional Definition Functionality

December 20, 2018

The National Library of Medicine (NLM) Value Set Authority Center (VSAC), with support from the Centers for Medicare and Medicaid Services (CMS), is pleased to announce the launch of

Intensional value set definition functionality in the VSAC Authoring Tool

Through the VSAC Authoring user interface, value set authors can algorithmically define value sets with logical rule-based Boolean clauses and hierarchy operators, leveraging the structure and hierarchies of terminologies. Logically-defined value sets, combined with the value set author’s guidance, can incorporate future changes as terminologies evolve to add or remove concepts, increasing efficiency and accuracy of value set creation and maintenance.

This first deployment of VSAC Intensional Functionality provides support for hierarchy functions for several terminologies. Later in 2019 we will add intensional functionality for more terminologies, including RxNorm and LOINC®.

You can learn more in our VSAC Support Center: Create an Intensional Value Set

You can contribute to the improvement of this application by sending feedback and ideas to the NLM Support Center. We especially would love to hear from you about specific intensional value sets you want to be able to create in VSAC in the future using RxNorm or LOINC.


The National Library of Medicine (NLM) is a leader in research in biomedical informatics and data science and the world’s largest biomedical library. NLM conducts and supports research in methods for recording, storing, retrieving, preserving, and communicating health information. NLM creates resources and tools that are used billions of times each year by millions of people to access and analyze molecular biology, biotechnology, toxicology, environmental health, and health services information. Additional information is available at

Last Reviewed: December 20, 2018