# An Interoperable UMLS Terminology Service Using FHIR
Further, the user can write a reusable software program or use an existing library to parse the standard's structure to use the UMLS knowledge. As UMLS is recognized internationally and used in a wide range of applications, there is a need for a terminology service--a light-weight solution, when compared to the current UMLS installation process, which expresses its knowledge in an interoperable format using mature standard(s). The emerging interoperability standard that can represent healthcare data and also has the ability to express a semantic standard's metadata and its content is Fast Interoperability Health Resources (FHIR) [7; 8; 9]. FHIR is an emerging new member of the HL7 family, developed to meet healthcare data interoperability requirements, and it has the great benefit of it being relatively easy to implement and rapidly deploy FHIR compliant applications when compared to other existing standards. Some of the salient features of FHIR are as follows: data are captured and shared as resource-modular data units; integrated support to REST with well-defined guidelines [10] allowing developers to manage and manipulate the resources using an API; and FHIR extensions allow experts to extend the FHIR resource to meet new requirements. Furthermore, when compared with existing standards (e.g., HL7 Clinical Document Architecture (CDA) [11], HL7 V2 messaging [11], openEHR [12], etc. ), FHIR by design has the ability to represent semantic knowledge using FHIR terminology resources; other standards do not have any foundational support. FHIR's ability to represent semantic knowledge along with FHIR features, and the availability of open-source implementation of the FHIR standard, the HAPI library [13], makes the FHIR standard a prime candidate to be evaluated and used to represent UMLS knowledge. Other healthcare standards lack an open-source implementation of the standard's specification. The overall objective of this research is to implement a terminology service, which allows users to query and easily access the UMLS knowledge structured using the FHIR standard. An interoperable representation of UMLS knowledge allows any FHIR-compliant application to consume UMLS knowledge without the need to understand its native knowledge structure and inner workings. Towards this objective, this research presents the following: A detailed analysis of similarities and differences between UMLS's knowledge structure and FHIR ConceptMap, an FHIR terminology resource; A design of FHIR extensions to profile ConceptMap to align it with UMLS's knowledge structure, which then allows us to express UMLS knowledge as ConceptMap and implement the extensions using the HAPI library to demonstrate the validity of the research; Finally, it allows us to design and implement the proposed REST-based terminology service, named UMLS FHIR, using the HAPI library that allows users to query the desired UMLS knowledge and expresses it in an interoperable format using the profiled FHIR ConceptMap. The UMLS FHIR terminology service is available at [[http://umls.it.ilstu.edu/umlsfhiir/](http://umls.it.ilstu.edu/umlsfhiir/)]([http://umls.it.ilstu.edu/umlsfhiir/](http://umls.it.ilstu.edu/umlsfhiir/)), whereas the API which drives the service is available at [[http://umls.it.ilstu.edu/umlsfhiir/fhiir](http://umls.it.ilstu.edu/umlsfhiir/fhiir)]([http://umls.it.ilstu.edu/umlsfhiir/fhiir](http://umls.it.ilstu.edu/umlsfhiir/fhiir)). As like any other API, UMLS FHIR API endpoints can be called from any FHIR compliant application to consume the FHIR formatted knowledge. The terminology service presents a simple web interface, on top of UMLS FHIR API, to query UMLS, returning the results in the FHIR format. The service acts as a simple interoperable facade hiding the discussed UMLS complexities.