expression

{
  "resourceType" : "StructureDefinition",
  "id" : "valueset-expression",
  "extension" : [{
    "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-wg",
    "valueCode" : "vocab"
  },
  {
    "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-fmm",
    "valueInteger" : 1
  }],
  "url" : "http://hl7.org/fhir/StructureDefinition/valueset-expression",
  "identifier" : [{
    "system" : "urn:ietf:rfc:3986",
    "value" : "urn:oid:2.16.840.1.113883.4.642.5.1211"
  }],
  "version" : "5.0.0-ballot",
  "name" : "expression",
  "status" : "draft",
  "experimental" : false,
  "date" : "2020-12-28T16:55:11+11:00",
  "publisher" : "HL7",
  "description" : "An expression that provides an alternative definition of the content of the value set (compose). There are two different ways to use this expression extension: If both an expression (this extension) and a compose element is present, the compose is understood to the make the same statement as the expression. If there is no compose, the expression is the only definition of the value set, and the value set can only be processed by a server that understands the expression syntax, the expression is computable.",
  "fhirVersion" : "5.0.0",
  "mapping" : [{
    "identity" : "rim",
    "uri" : "http://hl7.org/v3",
    "name" : "RIM Mapping"
  }],
  "kind" : "complex-type",
  "abstract" : false,
  "context" : [{
    "type" : "element",
    "expression" : "ValueSet"
  }],
  "type" : "Extension",
  "baseDefinition" : "http://hl7.org/fhir/StructureDefinition/Extension",
  "derivation" : "constraint",
  "snapshot" : {
    "element" : [{
      "id" : "Extension",
      "path" : "Extension",
      "short" : "An alternative computable expression of the value set content",
      "definition" : "An expression that provides an alternative definition of the content of the value set (compose). There are two different ways to use this expression extension: If both an expression (this extension) and a compose element is present, the compose is understood to the make the same statement as the expression. If there is no compose, the expression is the only definition of the value set, and the value set can only be processed by a server that understands the expression syntax, the expression is computable.",
      "comment" : "The expression may be a reference or the actual expression, and is expected to be in a computable format. Use the [rules-text extension](extension-valueset-rules-text.html) for a non-computable expression of the value set definition (compose).",
      "min" : 0,
      "max" : "1",
      "base" : {
        "path" : "Extension",
        "min" : 0,
        "max" : "*"
      },
      "constraint" : [{
        "key" : "ele-1",
        "severity" : "error",
        "human" : "All FHIR elements must have a @value or children",
        "expression" : "hasValue() or (children().count() > id.count())",
        "xpath" : "@value|f:*|h:div",
        "source" : "http://hl7.org/fhir/StructureDefinition/Element"
      },
      {
        "key" : "ext-1",
        "severity" : "error",
        "human" : "Must have either extensions or value[x], not both",
        "expression" : "extension.exists() != value.exists()",
        "xpath" : "exists(f:extension)!=exists(f:*[starts-with(local-name(.), 'value')])",
        "source" : "http://hl7.org/fhir/StructureDefinition/Extension"
      }],
      "isModifier" : false
    },
    {
      "id" : "Extension.id",
      "path" : "Extension.id",
      "representation" : ["xmlAttr"],
      "short" : "Unique id for inter-element referencing",
      "definition" : "Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.",
      "min" : 0,
      "max" : "1",
      "base" : {
        "path" : "Element.id",
        "min" : 0,
        "max" : "1"
      },
      "type" : [{
        "extension" : [{
          "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-fhir-type",
          "valueUrl" : "id"
        }],
        "code" : "http://hl7.org/fhirpath/System.String"
      }],
      "isModifier" : false,
      "isSummary" : false,
      "mapping" : [{
        "identity" : "rim",
        "map" : "n/a"
      }]
    },
    {
      "id" : "Extension.extension",
      "path" : "Extension.extension",
      "slicing" : {
        "discriminator" : [{
          "type" : "value",
          "path" : "url"
        }],
        "description" : "Extensions are always sliced by (at least) url",
        "rules" : "open"
      },
      "short" : "Extension",
      "definition" : "An Extension",
      "min" : 0,
      "max" : "0",
      "base" : {
        "path" : "Element.extension",
        "min" : 0,
        "max" : "*"
      },
      "type" : [{
        "code" : "Extension"
      }],
      "constraint" : [{
        "key" : "ele-1",
        "severity" : "error",
        "human" : "All FHIR elements must have a @value or children",
        "expression" : "hasValue() or (children().count() > id.count())",
        "xpath" : "@value|f:*|h:div",
        "source" : "http://hl7.org/fhir/StructureDefinition/Element"
      },
      {
        "key" : "ext-1",
        "severity" : "error",
        "human" : "Must have either extensions or value[x], not both",
        "expression" : "extension.exists() != value.exists()",
        "xpath" : "exists(f:extension)!=exists(f:*[starts-with(local-name(.), \"value\")])",
        "source" : "http://hl7.org/fhir/StructureDefinition/Extension"
      }],
      "isModifier" : false,
      "isSummary" : false
    },
    {
      "id" : "Extension.url",
      "path" : "Extension.url",
      "representation" : ["xmlAttr"],
      "short" : "identifies the meaning of the extension",
      "definition" : "Source of the definition for the extension code - a logical name or a URL.",
      "comment" : "The definition may point directly to a computable or human-readable definition of the extensibility codes, or it may be a logical URI as declared in some other specification. The definition SHALL be a URI for the Structure Definition defining the extension.",
      "min" : 1,
      "max" : "1",
      "base" : {
        "path" : "Extension.url",
        "min" : 1,
        "max" : "1"
      },
      "type" : [{
        "extension" : [{
          "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-fhir-type",
          "valueUrl" : "uri"
        }],
        "code" : "http://hl7.org/fhirpath/System.String"
      }],
      "fixedUri" : "http://hl7.org/fhir/StructureDefinition/valueset-expression",
      "isModifier" : false,
      "isSummary" : false,
      "mapping" : [{
        "identity" : "rim",
        "map" : "N/A"
      }]
    },
    {
      "id" : "Extension.value[x]",
      "path" : "Extension.value[x]",
      "short" : "Value of extension",
      "definition" : "Value of extension - must be one of a constrained set of the data types (see [Extensibility](extensibility.html) for a list).",
      "min" : 1,
      "max" : "1",
      "base" : {
        "path" : "Extension.value[x]",
        "min" : 0,
        "max" : "1"
      },
      "type" : [{
        "code" : "Expression"
      }],
      "constraint" : [{
        "key" : "ele-1",
        "severity" : "error",
        "human" : "All FHIR elements must have a @value or children",
        "expression" : "hasValue() or (children().count() > id.count())",
        "xpath" : "@value|f:*|h:div",
        "source" : "http://hl7.org/fhir/StructureDefinition/Element"
      }],
      "isModifier" : false,
      "isSummary" : false,
      "mapping" : [{
        "identity" : "rim",
        "map" : "N/A"
      }]
    }]
  },
  "differential" : {
    "element" : [{
      "id" : "Extension",
      "path" : "Extension",
      "short" : "An alternative computable expression of the value set content",
      "definition" : "An expression that provides an alternative definition of the content of the value set (compose). There are two different ways to use this expression extension: If both an expression (this extension) and a compose element is present, the compose is understood to the make the same statement as the expression. If there is no compose, the expression is the only definition of the value set, and the value set can only be processed by a server that understands the expression syntax, the expression is computable.",
      "comment" : "The expression may be a reference or the actual expression, and is expected to be in a computable format. Use the [rules-text extension](extension-valueset-rules-text.html) for a non-computable expression of the value set definition (compose).",
      "min" : 0,
      "max" : "1"
    },
    {
      "id" : "Extension.extension",
      "path" : "Extension.extension",
      "max" : "0"
    },
    {
      "id" : "Extension.url",
      "path" : "Extension.url",
      "fixedUri" : "http://hl7.org/fhir/StructureDefinition/valueset-expression"
    },
    {
      "id" : "Extension.value[x]",
      "path" : "Extension.value[x]",
      "min" : 1,
      "type" : [{
        "code" : "Expression"
      }]
    }]
  }
}