1.12 標準用語とコードの使用法

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Many elements in the FHIR resources are assigned a type of code, Coding or CodeableConcept. These elements contain codes that are associated with defined meanings defined by frameworks of varying sophistication and size. In some simple cases, the set of codes is a enumeration, a short list defined specifically for the element. In other cases, the list of codes is taken from a large and complex terminology or ontology such as SNOMED-CT or OBO.

All these elements of type code, Coding or CodeableConcept are given a "binding name" that defines the set of possible codes that can be used in the element in question.

For simple elements with type code, the element is either bound to a code list - a list of defined codes, or the binding references some external standard that defines the set of valid codes that can be used (typical examples of references are Mime Types, Language Codes,UCUM, etc.).

The value of an element of type code SHALL be one of the codes included in the code list or defined by the reference. Code comparison is always case sensitive for codes unless the codes are defined by a reference, and the reference specifically states otherwise.

No other codes can be used in an instance. If the binding is a code list, the list of codes may be extended in subsequent releases of the specification. Profiles may state rules on which codes may be used in particular contexts, but cannot define new or additional codes for these elements.

For elements with type CodeableConcept or Coding, the binding refers to a Value Set that defines a list of concepts along with the code/system pairs that refer to them.

If the binding is not marked as an example binding (see below):

• Coding:, the system/code SHOULD be one of the codes in the value set.
• CodeableConcept: one of the coding elements SHOULD contain a system/code that is in the value set.

System values are always case sensitive. Different code systems make their own rules as to whether the codes they define are case sensitive or not. Note that all the codes defined by FHIR itself are case sensitive and must be used in the provided case (usually, but not always, lowercase).

Bindings to value sets provided as part of the specification are always specific to the version of the value set published with the specification. The value set may be sealed by defining a simple list of enumerated codes, or it may include codes by their properties, in which case the list of valid concepts may grow or change over time.

Profiles can redefine the binding and are able to be much more precise about exactly which codes can be used for these elements (seeBinding Control for more detail).

The value set binding may be labelled as an example bindings. Example bindings are provided where the element has a very broad meaning (such as List.code), or where there is not enough consensus about which code system to use. In these cases, an indicative value set of the kind of codes that could be used in the element is provided. Applications MAY choose to use these codes where appropriate.

Generally it is expected that jurisdictions, projects and vendors will work together to choose actual working value sets. Subsequent versions of FHIR may replace example value sets with full bindings if enough consensus emerges.

The following reference tables are provided to help implementers:

• Systems List: Some known system identifiers suitable for use in the system element of CodeableConcept, Coding, and Identifier elements
• Bindings List: a full list of the binding names defined for all FHIR resources
• Code systems: Code systems defined as part of this specification
• Value Sets: Value sets defined as part of this specification
• v2 Namespaces list: A list of v2 tables that can be used in resources
• v3 Namespaces list: A list of v3 code systems and value sets used in FHIR