# What is the role of a National Terminology Server? *Collection: Implementation Strategy* **Summary**: A National Terminology Server is both a technical tool and a strategic asset. It should be the single source of truth for terminologies, support direct use by simple apps, and allow larger systems to host local copies for better performance. This allows for keeping national and local content separated, provides a public sandbox to support learning and testing, and follows a regular release schedule, ensuring everyone stays aligned. *** ## Implementation dilemma Facilitating access to the terminology is a key element of any implementation strategy. A National Terminology Server (NTS) is a centrally operated standards-based service that houses authoritative, version-controlled copies of SNOMED CT and other code systems, such as ICD-10 or drug dictionaries. It fulfils three complementary roles: 1. **Distribution** – publishes every official release, reference set, and map through an automated syndication feed, providing a better alternative to manual downloads and ensuring all stakeholders consume identical content. 2. **Real-time terminology services** – the NTS[^1] exposes a standard API, usually based on HL7 FHIR, using the `$expand`, `$lookup`, `$validate-code`, `$translate` and `$subsumes` operations so that client systems can resolve codes, value sets, and cross-maps on demand. 3. **Capacity-building** – provides an open sandbox, training guides, and connectathon environments that lower the barrier to entry for implementers. Because network latency and high query volumes can affect clinical performance, most production EHRs cache the national content in a **local** Terminology Server instance while still subscribing to the NTS[^1] feed for incremental updates. It is essential to consider all of these functions and requirements when defining a comprehensive National Terminology Server (NTS[^1]) strategy. ## Implementation Strategy Secure terminology distribution portals, such as SNOMED International's MLDS (Member Licensing and Distribution System), play a key role in managing the licensing submission and approval process. However, the functions of manually downloading RF2 zip files on secure portals can be significantly improved by implementing an NTS[^1], streamlining terminology server setup, facilitating updates, and preventing version mismatches. This is why, since 2023, MLDS[^2] has incorporated terminology syndication features. Other modern NTS[^1] platforms (e.g., NHS England’s Terminology Server, the Australian National Clinical Terminology Service, and Canada Health Infoway’s new FHIR server) also publish machine-readable releases via REST APIs or syndicated S3 buckets, enabling vendors to script and automate the ingestion process. Additionally, an NTS can serve as a lightweight or early-stage clinical application that requires access to the terminology. For example, a public vaccination portal might validate incoming SNOMED CT codes directly against the national endpoint without hosting its own server. Meanwhile, large hospital networks typically mirror the content locally, deploying a very fast local Terminology Server that synchronizes content from the National Terminology Server. ### Terminology Services Scenarios | Scenario | Recommended approach | Rationale | | ------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------- | | **Publishing official releases** | Expose a read-only **syndication API** (bulk download or delta files) and version them with semantic tags, e.g., `2025-07-31`. | Supports fully automated mirror jobs and rollback if a hotfix is issued. | | **High-throughput clinical systems** | Deploy a **local mirror** (Snowstorm, Ontoserver, HAPI) behind the firewall; configure nightly or continuous pull from the NTS feed. | Guarantees sub-50 ms response times and permits local extensions without polluting the national dataset. | | **Mobile or low-bandwidth apps** | Bundle the minimal subset (GPS, IPS, or domain-specific refsets) and schedule background sync when connectivity is available. | Keeps the footprint small while maintaining compliance. | | **Education & hackathons** | Spin up an **open sandbox** with anonymised SNOMED CT content, pre-loaded tutorials and a Grafana / Prometheus dashboard for monitoring. | Shortens the learning curve and surfaces best-practice REST patterns. | *** ## References 1. [NHS England. Terminology Server – FHIR APIs](https://digital.nhs.uk/developer/api-catalogue/terminology-server-fhir) 2. [NHS England. What is a terminology server?](https://digital.nhs.uk/services/terminology-server) 3. [Australian Digital Health Agency. National Clinical Terminology Service](https://www.digitalhealth.gov.au/healthcare-providers/product-releases/snomed-ct-au-and-australian-medicines-terminology-june-2025-release) 4. [Canada Health Infoway. Terminology Gateway migration to FHIR Terminology Server](https://infocentral.infoway-inforoute.ca/en/tools/standards-tools/terminology-gateway) 5. [SNOMED International. Snowstorm – open-source FHIR Terminology Server](https://www.implementation.snomed.org/terminology-services) 6. [HL7 FHIR Terminology Systems](https://build.fhir.org/terminologies-systems.html) ## Learn More To learn more, please reach out to . 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