The CodeSystem resource is used to declare the existence of and describe a code system or code system supplement and its key properties, and optionally define a part or all of its content.

An absolute URI that is used to identify this code system when it is referenced in a specification, model, design or an instance; also called its canonical identifier. This SHOULD be globally unique and SHOULD be a literal address at which an authoritative instance of this code system is (or will be) published. This URL can be the target of a canonical reference. It SHALL remain the same when the code system is stored on different servers. This is used in Coding.system.

Allows the code system to be referenced by a single globally unique identifier.

Can be a urn:uuid: or a urn:oid: but real http: addresses are preferred. Multiple instances may share the same URL if they have a distinct version.

The determination of when to create a new version of a resource (same url, new version) vs. defining a new artifact is up to the author. Considerations for making this decision are found in Technical and Business Versions.

In some cases, the resource can no longer be found at the stated url, but the url itself cannot change. Implementations can use the meta.source element to indicate where the current master source of the resource can be found.

A formal identifier that is used to identify this code system when it is represented in other formats, or referenced in a specification, model, design or an instance.

Allows externally provided and/or usable business identifiers to be easily associated with the module.

Typically, this is used for identifiers that can go in an HL7 V3 II (instance identifier) data type, and can then identify this code system outside of FHIR, where it is not possible to use the logical URI. Note that HL7 defines at least three identifiers for many of its code systems - the FHIR canonical URL, the OID and the V2 Table 0396 mnemonic code.

The identifier that is used to identify this version of the code system when it is referenced in a specification, model, design or instance. This is an arbitrary value managed by the code system author and is not expected to be globally unique. For example, it might be a timestamp (e.g. yyyymmdd) if a managed version is not available. There is also no expectation that versions can be placed in a lexicographical sequence. This is used in Coding.version.

There may be different code system instances that have the same identifier but different versions. The version can be appended to the url in a reference to allow a reference to a particular business version of the code system with the format [url]|[version]. The version SHOULD NOT contain a '#' - see Business Version.

A natural language name identifying the code system. This name should be usable as an identifier for the module by machine processing applications such as code generation.

Support human navigation and code generation.

The name is not expected to be globally unique. The name should be a simple alphanumeric type name to ensure that it is machine-processing friendly.

A short, descriptive, user-friendly title for the code system.

This name does not need to be machine-processing friendly and may contain punctuation, white-space, etc.

The status of this code system. Enables tracking the life-cycle of the content.

Allows filtering of code systems that are appropriate for use versus not.

A Boolean value to indicate that this code system is authored for testing purposes (or education/evaluation/marketing) and is not intended to be used for genuine usage.

Enables experimental content to be developed following the same lifecycle that would be used for a production-level code system.

Allows filtering of code systems that are appropriate for use versus not.

The date (and optionally time) when the code system was published. The date must change when the business version changes and it must change if the status code changes. In addition, it should change when the substantive content of the code system changes.

Note that this is not the same as the resource last-modified-date, since the resource may be a secondary representation of the code system. Additional specific dates may be added as extensions or be found by consulting Provenances associated with past versions of the resource.

The name of the organization or individual responsible for the release and ongoing maintenance of the code system.

Helps establish the "authority/credibility" of the code system. May also allow for contact.

Usually an organization but may be an individual. The publisher (or steward) of the code system is the organization or individual primarily responsible for the maintenance and upkeep of the code system. This is not necessarily the same individual or organization that developed and initially authored the content. The publisher is the primary point of contact for questions or issues with the code system. This item SHOULD be populated unless the information is available from context.

Contact details to assist a user in finding and communicating with the publisher.

May be a web site, an email address, a telephone number, etc.

A free text natural language description of the code system from a consumer's perspective.

This description can be used to capture details such as comments about misuse, instructions for clinical use and interpretation, literature references, examples from the paper world, etc. It is not a rendering of the code system as conveyed in the 'text' field of the resource itself. This item SHOULD be populated unless the information is available from context (e.g. the language of the code system is presumed to be the predominant language in the place the code system was created).

The content was developed with a focus and intent of supporting the contexts that are listed. These contexts may be general categories (gender, age, ...) or may be references to specific programs (insurance plans, studies, ...) and may be used to assist with indexing and searching for appropriate code system instances.

Assist in searching for appropriate content.

When multiple useContexts are specified, there is no expectation that all or any of the contexts apply.

A legal or geographic region in which the code system is intended to be used.

It may be possible for the code system to be used in jurisdictions other than those for which it was originally designed or intended.

Explanation of why this code system is needed and why it has been designed as it has.

This element does not describe the usage of the code system. Instead, it provides traceability of ''why'' the resource is either needed or ''why'' it is defined as it is. This may be used to point to source materials or specifications that drove the structure of this code system.

A copyright statement relating to the code system and/or its contents. Copyright statements are generally legal restrictions on the use and publishing of the code system.

Consumers must be able to determine any legal restrictions on the use of the code system and/or its content.

... Sometimes, the copyright differs between the code system and the codes that are included. The copyright statement should clearly differentiate between these when required.

The date on which the resource content was approved by the publisher. Approval happens once when the content is officially approved for usage.

The 'date' element may be more recent than the approval date because of minor changes or editorial corrections.

The date on which the resource content was last reviewed. Review happens periodically after approval but does not change the original approval date.

Gives a sense of how "current" the content is. Resources that have not been reviewed in a long time may have a risk of being less appropriate/relevant.

If specified, this date follows the original approval date.

The period during which the CodeSystem content was or is planned to be in active use.

Allows establishing a transition before a resource comes into effect and also allows for a sunsetting process when new versions of the CodeSystem are or are expected to be used instead.

The effective period for a CodeSystem determines when the content is applicable for usage and is independent of publication and review dates. For example, a measure intended to be used for the year 2016 might be published in 2015.

Descriptions related to the content of the CodeSystem. Topics provide a high-level categorization as well as keywords for the CodeSystem that can be useful for filtering and searching.

Repositories must be able to determine how to categorize the CodeSystem so that it can be found by topical and keyword searches.

This element provides topical categorization and keywords for the CodeSystem, as opposed to the more structured context-of-use information provided in the useContext element

An individiual or organization primarily involved in the creation and maintenance of the CodeSystem.

An individual or organization primarily responsible for internal coherence of the CodeSystem.

An individual or organization primarily responsible for review of some aspect of the CodeSystem.

An individual or organization responsible for officially endorsing the CodeSystem for use in some setting.

Related artifacts such as additional documentation, justification, dependencies, bibliographic references, and predecessor and successor artifacts.

A CodeSystem must be able to provide enough information for consumers of the content (and/or interventions or results produced by the content) to be able to determine and understand the justification for and evidence in support of the content.

Each related artifact is either an attachment, or a reference to another resource, but not both.

If code comparison is case sensitive when codes within this system are compared to each other.

If this value is missing, then it is not specified whether a code system is case sensitive or not. When the rule is not known, Postel's law should be followed: produce codes with the correct case, and accept codes in any case. This element is primarily provided to support validation software.

Canonical reference to the value set that contains all codes in the code system independent of code status.

The definition of the value set SHALL include all codes from this code system, independent of concept status, and only codes from this code system. It SHALL be immutable, and operations SHOULD support validation of any allowed code compositions.

The meaning of the hierarchy of concepts as represented in this resource.

Note that other representations might have a different hierarchy or none at all, and represent the information using properties.

The code system defines a compositional (post-coordination) grammar.

Note that the code system resource does not define what the compositional grammar is, only whether or not there is one.

This flag is used to signify that the code system does not commit to concept permanence across versions. If true, a version must be specified when referencing this code system.

Best practice is that code systems do not redefine concepts, or that if concepts are redefined, a new code system definition is created. But this is not always possible, so some code systems may be defined as 'versionNeeded'.

Most code systems occasionally refine the displays defined for concepts between versions. Contexts in which the concept display values are validated may require that the version be specified for some code systems irrespective of the value of this property.

The extent of the content of the code system (the concepts and codes it defines) are represented in this resource instance.

The canonical URL of the code system that this code system supplement is adding designations and properties to.

The most common use of a code system supplement is to add additional language support.

The total number of concepts defined by the code system. Where the code system has a compositional grammar, the basis of this count is defined by the system steward.

The count of concepts defined in this resource cannot be more than this value but may be less for several reasons - see the content element.

A filter that can be used in a value set compose statement when selecting concepts using a filter.

Note that filters defined in code systems usually require custom code on the part of any terminology engine that will make them available for use in value set filters. For this reason, they are generally only seen in high value published terminologies.

The code that identifies this filter when it is used as a filter in ValueSet.compose.include.filter.

A description of how or why the filter is used.

A list of operators that can be used with the filter.

A description of what the value for the filter should be.

A property defines an additional slot through which additional information can be provided about a concept.

Multiple occurrences of CodeSystem.concept.property may occur for a CodeSystem.property where CodeSystem.concept.property.code is the same and CodeSystem.concept.property.value differs. For example: multiple designations for a single concept.

A code that is used to identify the property. The code is used internally (in CodeSystem.concept.property.code) and also externally, such as in property filters.

Reference to the formal meaning of the property. One possible source of meaning is the Concept Properties code system.

A description of the property- why it is defined, and how its value might be used.

The type of the property value. Properties of type "code" contain a code defined by the code system (e.g. a reference to another defined concept).

Concepts that are in the code system. The concept definitions are inherently hierarchical, but the definitions must be consulted to determine what the meanings of the hierarchical relationships are.

If this is empty, it means that the code system resource does not represent the content of the code system.

A code - a text symbol - that uniquely identifies the concept within the code system.

A human readable string that is the recommended default way to present this concept to a user.

The formal definition of the concept. The code system resource does not make formal definitions required, because of the prevalence of legacy systems. However, they are highly recommended, as without them there is no formal meaning associated with the concept.

Additional representations for the concept - other languages, aliases, specialized purposes, used for particular purposes, etc.

Many concept definition systems support multiple representations, in multiple languages, and for multiple purposes.

Concepts have both a display and an array of designation. The display is equivalent to a special designation with an implied designation.use of "primary code" and a language equal to the Resource Language.

The language this designation is defined for.

In the absence of a language, the resource language applies.

A code that details how this designation would be used.

If no use is provided, the designation can be assumed to be suitable for general display to a human user.

Additional codes that detail how this designation would be used, if there is more than one use.

This was added rather than increasing the cardinality of .use to 0..* in order to maintain backward compatibility.

The text value for this designation.

A property value for this concept.

A code that is a reference to CodeSystem.property.code.

The value of this property.

Defines children of a concept to produce a hierarchy of concepts. The nature of the relationships is variable (is-a/contains/categorizes) - see hierarchyMeaning.