Release 5 Ballot

This page is part of the FHIR Specification (v5.0.0-ballot: FHIR R5 Ballot Preview). The current version which supercedes this version is 5.0.0. For a full list of available versions, see the Directory of published versions . Page versions: R5 R4B R4 R3 R2

Example StructureDefinition/Duration (XML)

Modeling and Methodology Work GroupMaturity Level: N/AStandards Status: Informative

Raw XML (canonical form + also see XML Format Specification)

StructureDefinition for Duration

<?xml version="1.0" encoding="UTF-8"?>

<StructureDefinition xmlns="http://hl7.org/fhir">
  <id value="Duration"/> 
  <text> 
    <status value="generated"/> 
    <div xmlns="http://www.w3.org/1999/xhtml">
      <table border="0" cellpadding="0" cellspacing="0" style="border: 0px #F0F0F0 solid; font-size: 11px; font-family: verdana; vertical-align: top;">
        <tr style="border: 1px #F0F0F0 solid; font-size: 11px; font-family: verdana; vertical-align: top">
          <th class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px">
            <a href="formats.html#table" title="The logical name of the element">Name</a> 
          </th> 
          <th class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px">
            <a href="formats.html#table" title="Information about the use of the element">Flags</a> 
          </th> 
          <th class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px">
            <a href="formats.html#table" title="Minimum and Maximum # of times the the element can appear in the instance">Card.</a> 
          </th> 
          <th class="hierarchy" style="width: 100px">
            <a href="formats.html#table" title="Reference to the type of the element">Type</a> 
          </th> 
          <th class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px">
            <a href="formats.html#table" title="Additional information about the element">Description &amp; Constraints</a> 
            <span style="float: right">
              <a href="formats.html#table" title="Legend for this format">
                <img alt="doco" src="help16.png" style="background-color: inherit"/> 
              </a> 
            </span> 
          </th> 
        </tr> 
        <tr style="border: 0px #F0F0F0 solid; padding:0px; vertical-align: top; background-color: white">
          <td class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px; white-space: nowrap; background-image: url(data:image/png;base64,iVBORw0KGg
          oAAAANSUhEUgAAAyAAAAACCAYAAACg/LjIAAAAI0lEQVR42u3QIQEAAAACIL/6/4MvTAQOkLYBAAB4kAAAANwMad9AqkRjgNAAAAA
          ASUVORK5CYII=)">
            <img alt="." class="hierarchy" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAWCAYAAAABxvaqAAAACXBIWXMAAAsTAAALEwEAmpwYAAAAB3
            RJTUUH3wYeFzIs1vtcMQAAAB1pVFh0Q29tbWVudAAAAAAAQ3JlYXRlZCB3aXRoIEdJTVBkLmUHAAAAE0lEQVQI12P4//8/AxMDAwN
            dCABMPwMo2ctnoQAAAABJRU5ErkJggg==" style="background-color: inherit"/> 
            <img alt="." class="hierarchy" src="data:image/png;base64,R0lGODlhEAAQAPZ/APrkusOiYvvfqbiXWaV2G+jGhdq1b8GgYf3v1frw3vTUlsWkZNewbcSjY/DQka
            d4Hb6dXv3u0f3v1ObEgfPTlerJiP3w1v79+e7OkPrfrfnjuNOtZPrpydaxa+/YrvvdpP779ZxvFPvnwKKBQaFyF/369M2vdaqHRPz
            58/HNh/vowufFhfroxO3OkPrluv779tK0e6JzGProwvrow9m4eOnIifPTlPDPkP78+Naxaf3v0/zowfXRi+bFhLWUVv379/rnwPvs
            zv3rye3LiPvnv+3MjPDasKiIS/789/3x2f747eXDg+7Mifvu0tu7f+/QkfDTnPXWmPrjsvrjtPbPgrqZW+/QlPz48K2EMv36866OU
            Pvowat8Ivvgq/Pbrvzgq/PguvrgrqN0Gda2evfYm9+7d/rpw9q6e/LSku/Rl/XVl/LSlfrkt+zVqe7Wqv3x1/bNffbOf59wFdS6if
            3u0vrqyP3owPvepfXQivDQkO/PkKh9K7STVf779P///wD/ACH5BAEKAH8ALAAAAAAQABAAAAemgH+CgxeFF4OIhBdKGwFChYl/hYw
            bdkoBPnaQkosbG3d3VEpSUlonUoY1Gzo6QkI8SrGxWBOFG4uySgY5ZWR3PFy2hnaWZXC/PHcPwkpJk1ShoHcxhQEXSUmtFy6+0iSF
            VResrjoTPDzdcoU+F65CduVU6KAhhQa3F8Tx8nchBoYuqoTLZoAKFRIhqGwqJAULFx0GYpBQeChRIR4TJm6KJMhQRUSBAAA7" style="background-color: white; background-color: inherit" title="Data Type"/>  
            <a href="datatypes-definitions.html#Duration" title="Duration : A length of time.">Duration</a> 
          </td> 
          <td class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px">
            <a href="elementdefinition-definitions.html#ElementDefinition.isSummary" style="padding-left: 3px; padding-right: 3px; color: black; null" title="This element is included in summaries">Σ</a> 
            <a href="versions.html#std-process" style="padding-left: 3px; padding-right: 3px; border: 1px grey solid; font-weight: bold; color:
             black; background-color: #e6ffe6" title="Standards Status = Normative">N</a> 
          </td> 
          <td class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px"/> 
          <td class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px">
            <a href="datatypes.html#Quantity">Quantity</a> 
          </td> 
          <td class="hierarchy" style="vertical-align: top; text-align : left; background-color: white; border: 0px #F0F0F0 solid;
           padding:0px 4px 0px 4px">A length of time
            <br/>  
            <a href="valueset-duration-units.html" title="Appropriate units for Duration.">Common UCUM Codes for Duration</a>  (
            <a href="terminologies.html#extensible" title="To be conformant, the concept in this element SHALL be from the specified value set if
             any of the codes within the value set can apply to the concept being communicated.  If
             the value set does not cover the concept (based on human review), alternate codings (or,
             data type allowing, text) may be included instead.">Extensible</a>  but limited to 
            <a href="valueset-all-time-units.html">AllUCUMExpressionForTime</a> )
            <br/>  
            <span style="font-style: italic" title="drt-1">+ Rule: There SHALL be a code if there is a value and it SHALL be an expression of time.
                If system is present, it SHALL be UCUM.</span> 
            <br/>  
            <br/>  Elements defined in Ancestors: 
            <a href="types.html#Element" title="Unique id for the element within a resource (for internal references). This may be any
             string value that does not contain spaces.">id</a> , 
            <a href="types.html#Element" title="May be used to represent additional information that is not part of the basic definition
             of the element. To make the use of extensions safe and manageable, there is a strict set
             of governance  applied to the definition and use of extensions. Though any implementer
             can define an extension, there is a set of requirements that SHALL be met as part of the
             definition of the extension.">extension</a> , 
            <a href="datatypes.html#Quantity" title="The value of the measured amount. The value includes an implicit precision in the presentation
             of the value.">value</a> , 
            <a href="datatypes.html#Quantity" title="How the value should be understood and represented - whether the actual value is greater
             or less than the stated value due to measurement issues; e.g. if the comparator is &quot;&lt;&quot;
             , then the real value is &lt; stated value.">comparator</a> , 
            <a href="datatypes.html#Quantity" title="A human-readable form of the unit.">unit</a> , 
            <a href="datatypes.html#Quantity" title="The identification of the system that provides the coded form of the unit.">system</a> , 
            <a href="datatypes.html#Quantity" title="A computer processable form of the unit in some unit representation system.">code</a> 
          </td> 
        </tr> 

        <tr> 
          <td class="hierarchy" colspan="5">
            <br/>  
            <a href="formats.html#table" title="Legend for this format">
              <img alt="doco" src="help16.png" style="background-color: inherit"/>  Documentation for this format
            </a> 
          </td> 
        </tr> 
      </table> 
    </div> 
  </text> 
  <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-standards-status">
    <valueCode value="normative"/> 
  </extension> 
  <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-normative-version">
    <valueCode value="4.0.0"/> 
  </extension> 
  <url value="http://hl7.org/fhir/StructureDefinition/Duration"/> 
  <version value="5.0.0-ballot"/> 
  <name value="Duration"/> 
  <status value="active"/> 
  <experimental value="false"/> 
  <date value="2022-09-07T10:58:29+10:00"/> 
  <publisher value="HL7 FHIR Standard"/> 
  <contact> 
    <telecom> 
      <system value="url"/> 
      <value value="http://hl7.org/fhir"/> 
    </telecom> 
  </contact> 
  <description value="Duration Type: A length of time."/> 
  <fhirVersion value="5.0.0-ballot"/> 
  <mapping> 
    <identity value="rim"/> 
    <uri value="http://hl7.org/v3"/> 
    <name value="RIM Mapping"/> 
  </mapping> 
  <mapping> 
    <identity value="v2"/> 
    <uri value="http://hl7.org/v2"/> 
    <name value="HL7 v2 Mapping"/> 
  </mapping> 
  <kind value="complex-type"/> 
  <abstract value="false"/> 
  <type value="Duration"/> 
  <baseDefinition value="http://hl7.org/fhir/StructureDefinition/Quantity"/> 
  <derivation value="specialization"/> 
  <snapshot> 
    <element id="Duration">
      <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-standards-status">
        <valueCode value="normative"/> 
      </extension> 
      <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-normative-version">
        <valueCode value="4.0.0"/> 
      </extension> 
      <path value="Duration"/> 
      <short value="A length of time"/> 
      <definition value="A length of time."/> 
      <comment value="The context of use may frequently define what kind of quantity this is and therefore what
       kind of units can be used. The context of use may also restrict the values for the comparator."/> 
      <min value="0"/> 
      <max value="*"/> 
      <base> 
        <path value="Duration"/> 
        <min value="0"/> 
        <max value="*"/> 
      </base> 
      <constraint> 
        <key value="drt-1"/> 
        <severity value="error"/> 
        <human value="There SHALL be a code if there is a value and it SHALL be an expression of time.  If system
         is present, it SHALL be UCUM."/> 
        <expression value="code.exists() implies ((system = %ucum) and value.exists())"/> 
        <xpath value="(f:code or not(f:value)) and (not(exists(f:system)) or f:system/@value='http://unitsofmeasure.org')"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Duration"/> 
      </constraint> 
      <constraint> 
        <key value="ele-1"/> 
        <severity value="error"/> 
        <human value="All FHIR elements must have a @value or children"/> 
        <expression value="hasValue() or (children().count() &gt; id.count())"/> 
        <xpath value="@value|f:*|h:div"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Element"/> 
      </constraint> 
      <constraint> 
        <key value="qty-3"/> 
        <severity value="error"/> 
        <human value="If a code for the unit is present, the system SHALL also be present"/> 
        <expression value="code.empty() or system.exists()"/> 
        <xpath value="not(exists(f:code)) or exists(f:system)"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Quantity"/> 
      </constraint> 
      <isModifier value="false"/> 
      <binding> 
        <extension url="http://hl7.org/fhir/build/StructureDefinition/binding-definition">
          <valueString value="Appropriate units for Duration."/> 
        </extension> 
        <extension url="http://hl7.org/fhir/StructureDefinition/elementdefinition-maxValueSet">
          <valueCanonical value="http://hl7.org/fhir/ValueSet/all-time-units"/> 
        </extension> 
        <extension url="http://hl7.org/fhir/StructureDefinition/elementdefinition-bindingName">
          <valueString value="DurationUnits"/> 
        </extension> 
        <strength value="extensible"/> 
        <valueSet value="http://hl7.org/fhir/ValueSet/duration-units"/> 
      </binding> 
      <mapping> 
        <identity value="v2"/> 
        <map value="SN (see also Range) or CQ"/> 
      </mapping> 
      <mapping> 
        <identity value="rim"/> 
        <map value="PQ, IVL&lt;PQ&gt;, MO, CO, depending on the values"/> 
      </mapping> 
      <mapping> 
        <identity value="rim"/> 
        <map value="PQ, IVL&lt;PQ&gt; depending on the values"/> 
      </mapping> 
    </element> 
    <element id="Duration.id">
      <path value="Duration.id"/> 
      <representation value="xmlAttr"/> 
      <short value="Unique id for inter-element referencing"/> 
      <definition value="Unique id for the element within a resource (for internal references). This may be any
       string value that does not contain spaces."/> 
      <min value="0"/> 
      <max value="1"/> 
      <base> 
        <path value="Element.id"/> 
        <min value="0"/> 
        <max value="1"/> 
      </base> 
    <!--  Note: special primitive values have a FHIRPath system type. e.g. this is compiler magic
       (j)  -->
      <type> 
        <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-fhir-type">
          <valueUrl value="id"/> 
        </extension> 
        <code value="http://hl7.org/fhirpath/System.String"/> 
      </type> 
      <isModifier value="false"/> 
      <isSummary value="false"/> 
      <mapping> 
        <identity value="rim"/> 
        <map value="n/a"/> 
      </mapping> 
    </element> 
    <element id="Duration.extension">
      <path value="Duration.extension"/> 
      <slicing> 
        <discriminator> 
          <type value="value"/> 
          <path value="url"/> 
        </discriminator> 
        <description value="Extensions are always sliced by (at least) url"/> 
        <rules value="open"/> 
      </slicing> 
      <short value="Additional content defined by implementations"/> 
      <definition value="May be used to represent additional information that is not part of the basic definition
       of the element. To make the use of extensions safe and manageable, there is a strict set
       of governance  applied to the definition and use of extensions. Though any implementer
       can define an extension, there is a set of requirements that SHALL be met as part of the
       definition of the extension."/> 
      <comment value="There can be no stigma associated with the use of extensions by any application, project,
       or standard - regardless of the institution or jurisdiction that uses or defines the extensions.
        The use of extensions is what allows the FHIR specification to retain a core level of
       simplicity for everyone."/> 
      <alias value="extensions"/> 
      <alias value="user content"/> 
      <min value="0"/> 
      <max value="*"/> 
      <base> 
        <path value="Element.extension"/> 
        <min value="0"/> 
        <max value="*"/> 
      </base> 
      <type> 
        <code value="Extension"/> 
      </type> 
      <constraint> 
        <key value="ele-1"/> 
        <severity value="error"/> 
        <human value="All FHIR elements must have a @value or children"/> 
        <expression value="hasValue() or (children().count() &gt; id.count())"/> 
        <xpath value="@value|f:*|h:div"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Element"/> 
      </constraint> 
      <constraint> 
        <key value="ext-1"/> 
        <severity value="error"/> 
        <human value="Must have either extensions or value[x], not both"/> 
        <expression value="extension.exists() != value.exists()"/> 
        <xpath value="exists(f:extension)!=exists(f:*[starts-with(local-name(.), &quot;value&quot;)])"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Extension"/> 
      </constraint> 
      <isModifier value="false"/> 
      <isSummary value="false"/> 
      <mapping> 
        <identity value="rim"/> 
        <map value="n/a"/> 
      </mapping> 
    </element> 
    <element id="Duration.value">
      <path value="Duration.value"/> 
      <short value="Numerical value (with implicit precision)"/> 
      <definition value="The value of the measured amount. The value includes an implicit precision in the presentation
       of the value."/> 
      <comment value="The implicit precision in the value should always be honored. Monetary values have their
       own rules for handling precision (refer to standard accounting text books)."/> 
      <requirements value="Precision is handled implicitly in almost all cases of measurement."/> 
      <min value="0"/> 
      <max value="1"/> 
      <base> 
        <path value="Quantity.value"/> 
        <min value="0"/> 
        <max value="1"/> 
      </base> 
      <type> 
        <code value="decimal"/> 
      </type> 
      <constraint> 
        <key value="ele-1"/> 
        <severity value="error"/> 
        <human value="All FHIR elements must have a @value or children"/> 
        <expression value="hasValue() or (children().count() &gt; id.count())"/> 
        <xpath value="@value|f:*|h:div"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Element"/> 
      </constraint> 
      <isModifier value="false"/> 
      <isSummary value="true"/> 
      <mapping> 
        <identity value="v2"/> 
        <map value="SN.2  / CQ - N/A"/> 
      </mapping> 
      <mapping> 
        <identity value="rim"/> 
        <map value="PQ.value, CO.value, MO.value, IVL.high or IVL.low depending on the value"/> 
      </mapping> 
    </element> 
    <element id="Duration.comparator">
      <path value="Duration.comparator"/> 
      <short value="&lt; | &lt;= | &gt;= | &gt; | ad - how to understand the value"/> 
      <definition value="How the value should be understood and represented - whether the actual value is greater
       or less than the stated value due to measurement issues; e.g. if the comparator is &quot;&lt;&quot;
       , then the real value is &lt; stated value."/> 
      <requirements value="Need a framework for handling measures where the value is &lt;5ug/L or &gt;400mg/L due
       to the limitations of measuring methodology."/> 
      <min value="0"/> 
      <max value="1"/> 
      <base> 
        <path value="Quantity.comparator"/> 
        <min value="0"/> 
        <max value="1"/> 
      </base> 
      <type> 
        <code value="code"/> 
      </type> 
      <meaningWhenMissing value="If there is no comparator, then there is no modification of the value"/> 
      <constraint> 
        <key value="ele-1"/> 
        <severity value="error"/> 
        <human value="All FHIR elements must have a @value or children"/> 
        <expression value="hasValue() or (children().count() &gt; id.count())"/> 
        <xpath value="@value|f:*|h:div"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Element"/> 
      </constraint> 
      <isModifier value="true"/> 
      <isModifierReason value="This is labeled as &quot;Is Modifier&quot; because the comparator modifies the interpretation
       of the value significantly. If there is no comparator, then there is no modification of
       the value"/> 
      <isSummary value="true"/> 
      <binding> 
        <extension url="http://hl7.org/fhir/build/StructureDefinition/binding-definition">
          <valueString value="How the Quantity should be understood and represented."/> 
        </extension> 
        <extension url="http://hl7.org/fhir/StructureDefinition/elementdefinition-bindingName">
          <valueString value="QuantityComparator"/> 
        </extension> 
        <strength value="required"/> 
        <valueSet value="http://hl7.org/fhir/ValueSet/quantity-comparator|5.0.0-ballot"/> 
      </binding> 
      <mapping> 
        <identity value="v2"/> 
        <map value="SN.1  / CQ.1"/> 
      </mapping> 
      <mapping> 
        <identity value="rim"/> 
        <map value="IVL properties"/> 
      </mapping> 
    </element> 
    <element id="Duration.unit">
      <extension url="http://hl7.org/fhir/StructureDefinition/elementdefinition-translatable">
        <valueBoolean value="true"/> 
      </extension> 
      <extension url="http://hl7.org/fhir/StructureDefinition/elementdefinition-translatable">
        <valueBoolean value="true"/> 
      </extension> 
      <path value="Duration.unit"/> 
      <short value="Unit representation"/> 
      <definition value="A human-readable form of the unit."/> 
      <requirements value="There are many representations for units of measure and in many contexts, particular representations
       are fixed and required. I.e. mcg for micrograms."/> 
      <min value="0"/> 
      <max value="1"/> 
      <base> 
        <path value="Quantity.unit"/> 
        <min value="0"/> 
        <max value="1"/> 
      </base> 
      <type> 
        <code value="string"/> 
      </type> 
      <constraint> 
        <key value="ele-1"/> 
        <severity value="error"/> 
        <human value="All FHIR elements must have a @value or children"/> 
        <expression value="hasValue() or (children().count() &gt; id.count())"/> 
        <xpath value="@value|f:*|h:div"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Element"/> 
      </constraint> 
      <isModifier value="false"/> 
      <isSummary value="true"/> 
      <mapping> 
        <identity value="v2"/> 
        <map value="(see OBX.6 etc.) / CQ.2"/> 
      </mapping> 
      <mapping> 
        <identity value="rim"/> 
        <map value="PQ.unit"/> 
      </mapping> 
    </element> 
    <element id="Duration.system">
      <path value="Duration.system"/> 
      <short value="System that defines coded unit form"/> 
      <definition value="The identification of the system that provides the coded form of the unit."/> 
      <requirements value="Need to know the system that defines the coded form of the unit."/> 
      <min value="0"/> 
      <max value="1"/> 
      <base> 
        <path value="Quantity.system"/> 
        <min value="0"/> 
        <max value="1"/> 
      </base> 
      <type> 
        <code value="uri"/> 
      </type> 
      <condition value="qty-3"/> 
      <constraint> 
        <key value="ele-1"/> 
        <severity value="error"/> 
        <human value="All FHIR elements must have a @value or children"/> 
        <expression value="hasValue() or (children().count() &gt; id.count())"/> 
        <xpath value="@value|f:*|h:div"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Element"/> 
      </constraint> 
      <isModifier value="false"/> 
      <isSummary value="true"/> 
      <mapping> 
        <identity value="v2"/> 
        <map value="(see OBX.6 etc.) / CQ.2"/> 
      </mapping> 
      <mapping> 
        <identity value="rim"/> 
        <map value="CO.codeSystem, PQ.translation.codeSystem"/> 
      </mapping> 
    </element> 
    <element id="Duration.code">
      <extension url="http://hl7.org/fhir/build/StructureDefinition/no-binding">
        <valueBoolean value="true"/> 
      </extension> 
      <path value="Duration.code"/> 
      <short value="Coded form of the unit"/> 
      <definition value="A computer processable form of the unit in some unit representation system."/> 
      <comment value="The preferred system is UCUM, but SNOMED CT can also be used (for customary units) or
       ISO 4217 for currency.  The context of use may additionally require a code from a particular
       system."/> 
      <requirements value="Need a computable form of the unit that is fixed across all forms. UCUM provides this
       for quantities, but SNOMED CT provides many units of interest."/> 
      <min value="0"/> 
      <max value="1"/> 
      <base> 
        <path value="Quantity.code"/> 
        <min value="0"/> 
        <max value="1"/> 
      </base> 
      <type> 
        <code value="code"/> 
      </type> 
      <constraint> 
        <key value="ele-1"/> 
        <severity value="error"/> 
        <human value="All FHIR elements must have a @value or children"/> 
        <expression value="hasValue() or (children().count() &gt; id.count())"/> 
        <xpath value="@value|f:*|h:div"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Element"/> 
      </constraint> 
      <isModifier value="false"/> 
      <isSummary value="true"/> 
      <mapping> 
        <identity value="v2"/> 
        <map value="(see OBX.6 etc.) / CQ.2"/> 
      </mapping> 
      <mapping> 
        <identity value="rim"/> 
        <map value="PQ.code, MO.currency, PQ.translation.code"/> 
      </mapping> 
    </element> 
  </snapshot> 
  <differential> 
    <element id="Duration">
      <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-standards-status">
        <valueCode value="normative"/> 
      </extension> 
      <extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-normative-version">
        <valueCode value="4.0.0"/> 
      </extension> 
      <path value="Duration"/> 
      <short value="A length of time"/> 
      <definition value="A length of time."/> 
      <min value="0"/> 
      <max value="*"/> 
      <constraint> 
        <key value="drt-1"/> 
        <severity value="error"/> 
        <human value="There SHALL be a code if there is a value and it SHALL be an expression of time.  If system
         is present, it SHALL be UCUM."/> 
        <expression value="code.exists() implies ((system = %ucum) and value.exists())"/> 
        <xpath value="(f:code or not(f:value)) and (not(exists(f:system)) or f:system/@value='http://unitsofmeasure.org')"/> 
        <source value="http://hl7.org/fhir/StructureDefinition/Duration"/> 
      </constraint> 
      <binding> 
        <extension url="http://hl7.org/fhir/build/StructureDefinition/binding-definition">
          <valueString value="Appropriate units for Duration."/> 
        </extension> 
        <extension url="http://hl7.org/fhir/StructureDefinition/elementdefinition-maxValueSet">
          <valueCanonical value="http://hl7.org/fhir/ValueSet/all-time-units"/> 
        </extension> 
        <extension url="http://hl7.org/fhir/StructureDefinition/elementdefinition-bindingName">
          <valueString value="DurationUnits"/> 
        </extension> 
        <strength value="extensible"/> 
        <valueSet value="http://hl7.org/fhir/ValueSet/duration-units"/> 
      </binding> 
      <mapping> 
        <identity value="rim"/> 
        <map value="PQ, IVL&lt;PQ&gt; depending on the values"/> 
      </mapping> 
    </element> 
  </differential> 
</StructureDefinition>

Usage note: every effort has been made to ensure that the examples are correct and useful, but they are not a normative part of the specification.