SearchParameter

Introduction

Scope and Usage

A SearchParameter resource specifies a search parameter that may be used on the RESTful API to search or filter on a resource. The SearchParameter resource declares:

• how to typically refer to the search parameter from a client (SearchParameter.code)
• how the search parameter is to be understood by the server
• where in the source resource the parameter matches

Boundaries and Relationships

• Search Parameters are referred to by CapabilityStatement resources via the canonical URL for a search parameter (CapabilityStatement.rest.resource.searchParam.definition)
• Search Parameters can appear in an Implementation Guide to specify how resources can be found

Background and Context

Implementers should be familiar with the background and concepts described in Search on the RESTful API before working with this resource.

There is a registry of all Search Parameters.

Notes

Naming Conventions for Search Parameters

HL7-defined search parameters follow these naming conventions:

• Use lowercase letters with hyphens for multi-word parameters (kebab-case)
• Prefer shorter, more common terms when possible
• Be consistent across resources when the same concept is searched (e.g., authored for authoring dates)
• Avoid abbreviations unless widely understood
• Use singular forms unless the concept is inherently plural
• Use of a prefix underscore character (_) compliant with the rules of the Style Guide

Notes

• If the extension's context specifies multiple resources, they are represented with multiple elements in the SearchParameter.base array
• An expression like Resource.descendents.extension('extension-url').value is possible, but this is a low performance option for a server to evaluate, and search parameter expressions are performance sensitive

Use of FHIRPath in Expressions

• An expression like Resource.descendents().extension('extension-url').value is possible, but this is a low performance option for a server to evaluate, and search parameter expressions are performance sensitive
• While SearchParameter.expression allows for the full use of FHIRPath, including resolve() in a search parameter definition makes it difficult to support for transactional servers. For that reason, this specification does not define parameters that link across resource instance boundaries.
  This specification does use search parameters with resolve() to narrow types (e.g., Observation.subject.resolve() is Patient). We recommend that other specifications follow the same practice - chaining is the mechanism defined to search across resource boundaries.

Balloter feedback requested: We are seeking input on approaches to managing the balance between expressiveness and performance impact on servers from the use of various FHIRPath features in search parameter expressions.

SearchParameters on Extensions

The SearchParameter resource may be used to define searches on extensions. A simple definition defines the code, the base resource the extension can be found in, and a type, and an expression. Assume that the extension is http://example.org/fhir/StructureDefinition/extension-thumb-length which has a value that is a quantity, and that is used on patient, then an appropriate SearchParameter would be:

"code" : "thumb-length", "base" : ["Patient"], "type" : "quantity", "expression" : "Patient.extension('http://example.org/fhir/StructureDefinition/extension-thumb-length').value"

Servers MAY attempt to process expressions that just select the extension without the .value, but this is not required and may be discouraged or deprecated in the future.

Extensions may have multiple types with different search behaviors, so the type can be specifically selected:

"code" : "thumb-length-code", "base" : ["Patient"], "type" : "token", "expression" : "Patient.extension('http://example.org/fhir/StructureDefinition/extension-thumb-length').value.ofType(CodeableConcept)"

This example would select coded thumb lengths and index them only for the thumb-length-code search parameter. When an extension can have multiple types with incompatible search behavior, the search parameters have to do this. Note that is type casting the extension directly (e.g. Patient.extension('...').ofType(CodeableConcept)) will lead to an empty index, since the extension is not a CodeableConcept itself.

When extensions can be used in multiple places, these places are enumerated in the expression:

Patient.extension('http://example.org/fhir/StructureDefinition/extension-thumb-length').value | Patient.contact.extension('http://example.org/fhir/StructureDefinition/extension-thumb-length').value | Practitioner.extension('http://example.org/fhir/StructureDefinition/extension-thumb-length').value

Search Parameter Aliases

To support evolution toward consistent naming conventions while maintaining backward compatibility, SearchParameter resources MAY define one or more aliasCode values. These aliases represent suggested alternative codes that can be used to reference the search parameter in addition to the primary code value.

Usage Guidelines:

• Aliases should be used primarily for backward compatibility when standardizing parameter names
• Servers that declare support for a SearchParameter SHOULD accept all defined aliases in addition to the primary code
• New implementations SHOULD use the primary code rather than aliases
• Aliases are displayed in the SearchParameter registry and resource search parameter tables

Example: A search parameter previously named authoredon might be updated to use authored as the primary code (for consistency with other resources) while retaining authoredon as an alias for backward compatibility.

Deriving Search Parameters

When one SearchParameter has a derivedFrom referencing another SearchParameter, the following rules SHOULD be followed. Note that these rules are asserted as SHOULD rather than SHALL only because they were introduced after the resource became normative. Systems that fail to follow these rules are likely to result in unsafe interoperability.

A derived SearchParameter:

• SHOULD have the same experimental as the original SearchParameter
• SHOULD have the same type as the original SearchParameter
• SHOULD have the same processingMode as the original SearchParameter
• SHOULD NOT have values for multipleOr or multipleAnd that contradict a value stated in the original SearchParameter. I.e. If the base does not declare these, the derived SearchParameter can. However, if the base does declare them, the derived SearchParameter SHOULD have the same values.
• SHOULD have a target that is equivalent to or a subset of the original SearchParameter target
• SHOULD have comparator and modifier values that are the same as or a superset of those defined in the base.
• SHOULD have the same number of components listed in the same order, where the definition must be the same or a derived SearchParameter, and the expression must be the same.
• MAY add values for chain but SHOULD NOT remove or re-order values already listed in the base.

Request for ballot feedback: We would like the 'SHOULD' assertions above to become 'SHALL' assertions. We are invoking our usual implementer outreach process to find out whether anyone else objects, but please file tickets for any rules you do not believe can be enforced that way.

StructureDefinition

Elements (Simplified)

• SearchParameter [0..*]: - Search parameter for a resource
• SearchParameter.url [1..1]: uri Canonical identifier for this search parameter, represented as a URI (globally unique)
• SearchParameter.identifier [0..*]: Identifier Additional identifier for the search parameter (business identifier)
• SearchParameter.version [0..1]: string Business version of the search parameter
• SearchParameter.versionAlgorithm[x] [0..1]: string, Coding extensible:version-algorithm How to compare versions
• SearchParameter.name [1..1]: string Name for this search parameter (computer friendly)
• SearchParameter.title [0..1]: string Name for this search parameter (human friendly)
• SearchParameter.derivedFrom [0..1]: canonical Original definition for the search parameter
• SearchParameter.status [1..1]: code required:publication-status draft | active | retired | unknown
• SearchParameter.experimental [0..1]: boolean For testing only - never for real usage
• SearchParameter.date [0..1]: dateTime Date last changed
• SearchParameter.publisher [0..1]: string Name of the publisher/steward (organization or individual)
• SearchParameter.contact [0..*]: ContactDetail Contact details for the publisher
• SearchParameter.description [1..1]: markdown Natural language description of the search parameter
• SearchParameter.useContext [0..*]: UsageContext The context that the content is intended to support
• SearchParameter.jurisdiction [0..*]: CodeableConcept extensible:jurisdiction Jurisdiction of the authority that maintains the search parameter (if applicable)
• SearchParameter.purpose [0..1]: markdown Why this search parameter is defined
• SearchParameter.copyright [0..1]: markdown Notice about intellectual property ownership, can include restrictions on use
• SearchParameter.copyrightLabel [0..1]: string Copyright holder and year(s)
• SearchParameter.code [1..1]: code Recommended name for parameter in search url
• SearchParameter.aliasCode [0..*]: code Additional recommended names for parameter in search url
• SearchParameter.base [1..*]: code required:version-independent-all-resource-types The resource type(s) this search parameter applies to
• SearchParameter.type [1..1]: code required:search-param-type number | date | string | token | reference | composite | quantity | uri | special | resource
• SearchParameter.expression [0..1]: string FHIRPath expression that extracts the values
• SearchParameter.processingMode [0..1]: code required:search-processingmode normal | phonetic | other
• SearchParameter.constraint [0..1]: string FHIRPath expression that constraints the usage of this SearchParameter
• SearchParameter.target [0..*]: code required:version-independent-all-resource-types Types of resource (if a resource reference)
• SearchParameter.multipleOr [0..1]: boolean Allow multiple values per parameter (or)
• SearchParameter.multipleAnd [0..1]: boolean Allow multiple parameters (and)
• SearchParameter.comparator [0..*]: code required:search-comparator eq | ne | gt | lt | ge | le | sa | eb | ap
• SearchParameter.modifier [0..*]: code required:search-modifier-all-codes missing | exact | contains | not | text | in | not-in | below | above | type | identifier | of-type | code-text | text-advanced | iterate
• SearchParameter.chain [0..*]: string Chained names supported
• SearchParameter.component [0..*]: BackboneElement For Composite resources to define the parts
• SearchParameter.component.definition [1..1]: canonical Defines how the part works
• SearchParameter.component.expression [1..1]: string Sub-expression relative to main expression

Mappings

• SearchParameter Mappings — 13 mapping entries

Implementation Guide

implementationguide-SearchParameter-core.xml

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

<ImplementationGuide xmlns="http://hl7.org/fhir">
  <id value="SearchParameter-core"/>
  <name value="StandardSearchParameterExtensions"/>
  <title value="Standard  Search  Parameter  Extensions"/>
  <status value="draft"/>
  <date value="2014-01-31T00:00:00.000"/>
  <publisher value="Health Level Seven, Inc. - [WG Name] WG"/>
  <description value="This profile describes common extensions that are used with Search Parameters"/>
</ImplementationGuide>

Resource Packs

list-SearchParameter-packs.xml

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

<List xmlns="http://hl7.org/fhir">
  <id value="SearchParameter-packs"/>
  <status value="current"/>
  <mode value="working"/>
  <entry>
    <item>
      <reference value="ImplementationGuide/SearchParameter-core"/>
    </item>
  </entry>
</List>

Search Parameters

• base — token — The resource type(s) this search parameter applies to — SearchParameter.base
• code — token — Code used in URL — SearchParameter.code
• component — reference — Defines how the part works — SearchParameter.component.definition
• context — token — A use context assigned to the search parameter — (SearchParameter.useContext.value.ofType(CodeableConcept))
• context-quantity — quantity — A quantity- or range-valued use context assigned to the search parameter — (SearchParameter.useContext.value.ofType(Quantity)) | (SearchParameter.useContext.value.ofType(Range))
• context-type — token — A type of use context assigned to the search parameter — SearchParameter.useContext.code
• context-type-quantity — composite — A use context type and quantity- or range-based value assigned to the search parameter — SearchParameter.useContext
• context-type-value — composite — A use context type and value assigned to the search parameter — SearchParameter.useContext
• date — date — The search parameter publication date — SearchParameter.date
• derived-from — reference — Original definition for the search parameter — SearchParameter.derivedFrom
• description — string — The description of the search parameter — SearchParameter.description
• identifier — token — External identifier for the search parameter — SearchParameter.identifier
• identifier — token — External identifier for the search parameter — SearchParameter.identifier
• jurisdiction — token — Jurisdiction of the authority that maintains the the search parameter — SearchParameter.jurisdiction
• name — string — Computationally friendly name of the search parameter — SearchParameter.name
• publisher — string — Name of the publisher of the search parameter — SearchParameter.publisher
• status — token — The current status of the search parameter — SearchParameter.status
• target — token — Types of resource (if a resource reference) — SearchParameter.target
• type — token — number | date | string | token | reference | composite | quantity | uri | special — SearchParameter.type
• url — uri — The uri that identifies the search parameter — SearchParameter.url
• version — token — The business version of the search parameter — SearchParameter.version
• experimental — token — Whether the SearchParameter is experimental — SearchParameter.experimental

Full Search Parameters

Examples

• example — searchparameter-example — General example
• example-constraint — searchparameter-example-constraint — Search parameter for constraint example
• example-extension — searchparameter-example-extension — Search parameter for an extension example
• example-reference — searchparameter-example-reference — Search parameter for a reference example
• filter — searchparameter-filter — Formal Definition for _filter parameter
• searchparameter-example — searchparameter-example
• searchparameter-example-constraint — searchparameter-example-constraint
• searchparameter-example-extension — searchparameter-example-extension
• searchparameter-example-reference — searchparameter-example-reference
• searchparameter-examples-header — searchparameter-examples-header

Full Examples

Mapping Exceptions

searchparameter-fivews-mapping-exceptions.xml

Unmapped Elements

• FiveWs.what — Not relevant for this resource
• FiveWs.author — Not relevant for this resource
• FiveWs.actor — Not relevant for this resource
• FiveWs.cause — Not relevant for this resource
• FiveWs.where — Not relevant for this resource
• FiveWs.context — Not relevant for this resource
• FiveWs.init — Not relevant for this resource
• FiveWs.source — Not relevant for this resource
• FiveWs.who — Not relevant for this resource
• FiveWs.grade — Not relevant for this resource
• FiveWs.planned — Not relevant for this resource
• FiveWs.done — Not relevant for this resource
• FiveWs.subject — Not relevant for this resource