The FHIR (Fast Healthcare Interoperability Resources) terminology specification is based on two key concepts:
– code system – declares the existence of and describes a code system or code system supplement and its key properties, and optionally defines a part or all of its content. Also known as Ontology, Terminology, or Enumeration
– value set – specifies a set of codes drawn from one or more code systems, intended for use in a particular context. Value sets link between CodeSystem definitions and their use in coded elements
Code systems define which codes (symbols and/or expressions) exist, and how they are understood. Value sets select a set of codes from one or more code systems to specify which codes can be used in a particular context.
The CodeSystem resource is used to declare the existence of a code system, and its key properties:
– Identifying URL and version
– Description, Copyright, publication date, and other metadata
– Some key properties of the code system itself – e.g. whether it exhibits concept permanence, whether it defines a compositional grammar, and whether the codes that it defines are case sensitive
– What filters can be used in value sets that use the code system in a ValueSet.compose element
– What concept properties are defined by the code system
– In addition, the CodeSystem resource may list some or all of the concepts in the code system, along with their basic properties (code, display, definition), designations, and additional properties. Code System resources may also be used to define supplements, which extend an existing code system with additional designations and properties.
The CodeSystem resource is not intended to support the process of maintaining code systems. Instead, the focus is on publishing the properties and optionally the content of a code system for use throughout the FHIR eco-system, such as to support value set expansion and validation. Note that the important existing (large) code systems (SNOMED CT, LOINC, RxNorm, ICD family, etc.) all have their own maintenance systems and distribution formats, and CodeSystem is generally not an efficient way to distribute their content, though it is used as one way of declaring the filters and properties associated with those code systems.
Fast Healthcare Interoperability Resources (FHIR) is a draft standard describing data formats and elements (known as “resources”) and an application programming interface (API) for exchanging electronic health records. The standard was created by the Health Level Seven International (HL7) health-care standards organization.
Its goal is to facilitate interoperation between legacy healthcare systems, to make it easy to provide healthcare information to healthcare providers and individuals on a wide variety of devices from computers to tablets to cell phones, and to allow third-party application developers to provide medical applications which can be easily integrated into existing systems.
FHIR provides an alternative to document-centric approaches by directly exposing discrete data elements as services. For example, basic elements of healthcare like patients, admissions, diagnostic reports and medications can each be retrieved and manipulated via their own resource URLs (Uniform Resource Locators). FHIR was supported at an American Medical Informatics Association meeting by many EHR (Electronic Health Record) vendors which value its open and extensible nature.