<ValueSet xmlns="http://hl7.org/fhir"&gt; 
 <!– from Resource: id, meta, implicitRules, and language –>
 <!– from DomainResource: text, contained, extension, and modifierExtension –>
 <identifier value="[uri]"/><!– 0..1 Globally unique logical id for  value set –>
 <version value="[string]"/><!– 0..1 Logical id for this version of the value set –>
 <name value="[string]"/><!– 0..1 Informal name for this value set –>
 <purpose value="[string]"/><!– 0..1 Textual description of the intended scope and use –>
 <immutable value="[boolean]"/><!– 0..1 Indicates whether or not any change to the content logical definition may occur –>
 <publisher value="[string]"/><!– 0..1 Name of the publisher (Organization or individual) –>
 <telecom><!– 0..* ContactPoint Contact information of the publisher –></telecom>
 <description value="[string]"/><!– 0..1 Human language description of the value set –>
 <copyright value="[string]"/><!– 0..1 Publishing restrictions for the value set –>
 <status value="[code]"/><!– 1..1 draft | active | retired –>
 <experimental value="[boolean]"/><!– 0..1 If for testing purposes, not real usage –>
 <extensible value="[boolean]"/><!– 0..1 Whether this is intended to be used with an extensible binding –>
 <date value="[dateTime]"/><!– 0..1 Date for given status –>
 <stableDate value="[date]"/><!– 0..1 Fixed date for the version of all referenced code systems and value sets –>
 <define>  <!–  0..1 When value set defines its own codes –>
  <system value="[uri]"/><!– 1..1 URI to identify the code system –>
  <version value="[string]"/><!– 0..1 Version of this system –>
  <caseSensitive value="[boolean]"/><!– 0..1 If code comparison is case sensitive –>
  <concept>  <!– 0..* Concepts in the code system –>
   <code value="[code]"/><!– 1..1 Code that identifies concept –>
   <abstract value="[boolean]"/><!– 0..1 If this code is not for use as a real concept –>
   <display value="[string]"/><!– 0..1 Text to Display to the user –>
   <definition value="[string]"/><!– 0..1 Formal Definition –>
   <designation>  <!– 0..* Additional representations for the concept –>
    <language value="[code]"/><!– 0..1 Language of the designation –>
    <use><!– 0..1 Coding Details how this designation would be used –></use>
    <value value="[string]"/><!– 1..1 The text value for this designation –>
   </designation>
   <concept><!– 0..* Content as for ValueSet.define.concept Child Concepts (is-a / contains) –></concept>
  </concept>
 </define>
 <compose>  <!–  0..1 When value set includes codes from elsewhere –>
  <import value="[uri]"/><!–  0..* Import the contents of another value set –>
  <include>  <!–  0..* Include one or more codes from a code system –>
   <system value="[uri]"/><!– 1..1 The system the codes come from –>
   <version value="[string]"/><!– 0..1 Specific version of the code system referred to –>
   <concept>  <!– 0..* A concept defined in the system –>
    <code value="[code]"/><!– 1..1 Code or expression from system –>
    <display value="[string]"/><!– 0..1 Test to display for this code for this value set –>
    <designation><!– 0..* Content as for ValueSet.define.concept.designation Additional representations for this valueset –></designation>
   </concept>
   <filter>  <!– 0..* Select codes/concepts by their properties (including relationships) –>
    <property value="[code]"/><!– 1..1 A property defined by the code system –>
    <op value="[code]"/><!– 1..1 = | is-a | is-not-a | regex | in | not in –>
    <value value="[code]"/><!– 1..1 Code from the system, or regex criteria –>
   </filter>
  </include>
  <exclude><!–  0..* Content as for ValueSet.compose.include Explicitly exclude codes –></exclude>
 </compose>
 <expansion>  <!–  0..1 Used when the value set is "expanded" –>
  <identifier><!– 0..1 Identifier Uniquely identifies this expansion –></identifier>
  <timestamp value="[dateTime]"/><!– 1..1 Time valueset expansion happened –>
  <contains>  <!– 0..* Codes in the value set –>
   <system value="[uri]"/><!– 0..1 System value for the code –>
   <abstract value="[boolean]"/><!– 0..1 If user cannot select this entry –>
   <version value="[string]"/><!– 0..1 Version in which this code / display is defined –>
   <code value="[code]"/><!–  0..1 Code - if blank, this is not a choosable code –>
   <display value="[string]"/><!–  0..1 User display for the concept –>
   <contains><!– 0..* Content as for ValueSet.expansion.contains Codes contained in this concept –></contains>
  </contains>
 </expansion>
</ValueSet>

Alternate definitions: Schema/Schematron,
Resource Profile (XML, JSON),
Questionnaire

6.22.4.1

Terminology Bindings

6.22.4.2 Constraints

• Inv-2: A value set with only one import SHALL also have an include and/or an exclude unless the value set defines its own codes (xpath: not(exists(f:compose)) or (count(f:compose/f:import)!=1 or exists(f:compose/f:include) or exists(f:compose/f:exclude) or exists(f:define)))
• Inv-5: Value set SHALL contain either a define, a compose, or an expansion element (xpath: exists(f:define) or exists(f:compose) or exists(f:expansion))
• Inv-7: A defined code system (if present) SHALL have a different identifier to the value set itself (xpath: not(exists(f:define)) or (f:define/f:system/@value != f:identifier/@value))
• Inv-3: On ValueSet.define: Within a code system definition, all the codes SHALL be unique (xpath on f:ValueSet/f:define: count(distinct-values(descendant::f:concept/f:code/@value))=count(descendant::f:concept))
• Inv-8: On ValueSet.define: Codes must be unique (xpath on f:ValueSet/f:define: count(descendant::f:concept)=count(distinct-values(descendant::f:concept/f:code/@value)))
• Inv-1: On ValueSet.compose: A value set composition SHALL have an include or an import (xpath on f:ValueSet/f:compose: exists(f:include) or exists(f:import))
• Inv-6: On ValueSet.expansion.contains: SHALL have a code or a display (xpath on f:ValueSet/f:expansion/f:contains: exists(f:code) or exists(f:display))
• Inv-9: On ValueSet.expansion.contains: Must have a code if not abstract (xpath on f:ValueSet/f:expansion/f:contains: exists(f:code) or (f:display/@value = ‘true’))
• Inv-10: On ValueSet.expansion.contains: Must have a system if a code is present (xpath on f:ValueSet/f:expansion/f:contains: exists(f:system) or not(exists(f:code)))

6.22.5 Identifier and Version

The identifier and version elements may be used to reference this value set in a design, a profile, a
CDA template or V3 message (valueSet and valueSetVersion). These different contexts may make additional restrictions
on the possible values of these elements. These elements are generally not needed when using value sets with FHIR
implementations as they can make use of the innate identifier and versioning mechanism associated with the resource

6.22.6 Value Sets that define codes

Valuesets can define their own codes. A value set that defines codes automatically includes all
the codes it defines, and is useful for simple sets of codes that are highly
specific and context-dependent. The value set and the code system are both
given URI identifiers by which they may be identified from elsewhere
(ValueSet.identifier and ValueSet.define.system). These identifiers SHALL
be different.

• ValueSet.define.system is the URI that identifies these codes when used in a Coding
• The usability of the codes is closely linked to the quality of the definitions. Although a definition is not required for each concept, a good definition SHOULD be provided. In the absence of any definition, there is no formal meaning associated with the concept
• If concepts contain other concepts, then the contained concepts are "subsumed" by the containing concept (there is an "is-a" relationship between the codes).
• An abstract concept SHALL have contained concepts
• The set of codes defined SHALL not contain duplicate codes

Note: Value sets only define their own codes when they are not defined elsewhere,
such as codes defined in SNOMED CT, LOINC, RxNorm etc. To specify a value set that
is made up of codes from other code systems, see "compose" below.

6.22.6.1 Versioning Code Systems

Most code systems evolve over time, due to corrections, clarifications, and changes to approach or underlying knowledge or reality.
If these changes lead to the meanings of existing codes changing significantly, then the interpretation of the code system becomes
version dependent. This significantly complicates implementation based on the code system, to the point where it is not clear that
safety can be assured, so SHOULD be avoided whenever possible. It is preferable to assign a new identifier to a code system
when any concepts in it have a significant change in meaning (for example, the German diagnostic classification code system
ICD10GM2009 has a different system to ICD10GM2008), but this also can have substantial impact on implementation, so
is often not practical - for instance, LOINC has re-defined the meaning of codes in the past,
but there is only one identifier for LOINC.

For this reason, a code system MAY provide a version identifer in ValueSet.define.version. The version specific identifier SHOULD be
provided whenever there are potentially significant changes in meaning across multiple releases of a code system.
There is no particular format requirement for the version identifier, though HL7 recommends a date based approach.

When the value set definition of a code system includes a version identifier, the version identifier SHOULD be
used in Coding instances that refer to the code system.

Where the terminology does not clearly define what string should be used to identify code system versions, the recommendation is to use the date (expressed in FHIR date format) on which that version was officially published as the version date.

6.22.7 Value Sets that include codes defined elsewhere

Value sets that include codes defined in some other code system are most useful when
dealing with large general code systems such as SNOMED CT, LOINC, RxNorm or various IETF code sets
including human language. The value set can be a simple list of included codes or it can be some
kind of general selection criteria using the facilities provided by the code system.

• Within an include or exclude criterion, multiple filters and concept selections are intersected. All the conditions specified SHALL be true.
• The value set always includes any codes it defines itself. A typical use for this
  is when including a set of codes from elsewhere, and adding a few additional codes to cover
  cases not catered to by the included codes
• An include statement consists of any enumerated codes and any codes that meet the filter criteria
• If the system reference is not version specific and filters are present, then the contents of the value set are open and change over time as the underlying code systems are updated
• The content of the value set is constructed by unioning of all the import and include statements and then eliminating any of the ‘excluded’ codes.

• A value set needs to do something. It can’t simply include an existing value set without also including additional content or excluding content

  * Using the property filters is only possible where the underlying code system defines appropriate properties. Note that in some cases, the underlying code system defines the logical concepts but not the syntax for exercising them. In such cases, the literal definitions may be provided by a third party. See below for notes about its use against common code systems

• Value sets may include abstract codes - that is, codes designated by the underlying code system as not for use as a real concept. These abstract codes are typically used as a grouping/searching mechanism,
  and can be included either by enumerating them, or by using a filter

When a value set enumerates codes, it is also able to define an alternative display for
the code that is to be used where ever the value set is expanded and used in a UI. This
facility is provided to cover the following circumstances:

• The system that defines the code or expression doesn’t provide a display for this code (or any codes)
• The system that defines the code or expression defines multiple choices for display
• The system provides a very long display name that is unnecssary or innappropriate in the context of this value set (e.g. a display name of "Glucose [Mass/volume] in Serum or Plasma –10 PM specimen" for LOINC code 48991-4, when the value set only includes Glucose mass/vol in serum/plasma codes). As the display names get longer, this becomes more important

Note that care must be taken in order to avoid "changing the meaning" of the concept by
implying that it means something other than the explicit definition of the concept in the
underlying system (e.g. in the case above, using a display "Glucose Concentration at 10pm").
For this reason, some contexts of use do not allow a display to be associated with a specific code.

The display name for the code in the value set is only used in the UI. The display in a
a Coding must be taken from the underlying system,
even if a value set is referenced explicitly in the Coding. The alternative display
specified in the value set would go in CodeableConcept.text.

6.22.7.1 Code systems Note

How filters are used with various code systems:

• LOINC: See Using LOINC with FHIR
• SNOMED-CT: See Using SNOMED CT with FHIR
• RxNorm: See Using RxNorm with FHIR
  
  
  
  
  
  
  
  
  
  

  System	Property Name	Operation	Value	Definition	Example

6.22.8 Value Set Expansion

A value set can be "expanded", where the definition of the value set is
used to create a simple collection of codes suitable for use for data
entry or validation. This is most useful when a value set includes
all the children of a code or a set of codes by filter.

A resource that represents a value set expansion includes the same
identification details as the definition of the value set, and MAY
include the definition of the value set (define and compose
elements). In addition it has a expansion element which contains
the list of codes that constitute the value set expansion. If the
expansion is heirarchical (codes contain other concepts), there
is no implication about the logical relationship between them; this
is guidance for helping human user navigate the choice of codes that
may or may not relate to the logical definitions of the codes or concepts.

In general, the following process should be followed when
expanding a value set:

• for each compose.import, find the referenced value set, expand that, and add it to the result set

• for each compose.include, identify the correct version of the code system, and then:

  *   if there is no codes or filters, add every code in the code system to the result set
  

  • if codes are listed, add them to the result set
  • if any filters are present, process them in order (as explained above), and add the intersection of their results to the result set
• for each compose.exclude, follow the same process as for compose.include, but remove any codes from the result set, instead of adding them
• add any codes in the define to the result set

The "result set" is then represented in expansion. Note that the expansion structure is inherently ordered, and
also provides support for a hierarchical tree of items. This specification does not fix the meaning of use of either
of these, and the conceptual approach described should not be understood to prohibit any implementation approach in
these regards. There is a defined operation to ask a server to perform this expansion.

An expansion may include entries in the expansion that only serve an arbitrary grouping purpose, to make it easier
for a human to use the list. These entries have no system or code, and must be marked as abstract. Note that the
value set define and compose offer no support for defining these, but this does not exclude servers from using
extensions or other knowledge to introduce such groups as an implementation feature.

6.22.9 Search Parameters

Search parameters for this resource. The common parameters also apply. See Searching for more information about searching in REST, messaging, and services.

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