A task to be performed.

A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content. Often, this is a reference to an implementation guide that defines the special rules along with other profiles etc.

Asserting this rule set restricts the content to be only understood by a limited set of trading partners. This inherently limits the usefulness of the data in the long term. However, the existing health eco-system is highly fractured, and not yet ready to define, collect, and exchange data in a generally computable sense. Wherever possible, implementers and/or specification writers should avoid using this element. Often, when used, the URL is a reference to an implementation guide that defines these special rules as part of it's narrative along with other profiles, value sets, etc.

An Extension

STU3: Task.definition[x] (new:Reference(ActivityDefinition), uri)

Element Task.definition[x] has a context of Task based on following the parent source element upwards and mapping to Task. Element Task.definition[x] has no mapping targets in FHIR R4B. Typically, this is because the element has been added (is a new element).

May be used to represent additional information that is not part of the basic definition of the resource and that modifies the understanding of the element that contains it and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. 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 is allowed to define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.

Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

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.

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

The current status of the task.

The current status of the task.

These states enable coordination of task status with off-the-shelf workflow solutions that support automation of tasks.

Indicates the "level" of actionability associated with the Task, i.e. i+R[9]Cs this a proposed task, a planned task, an actionable task, etc.

This element is immutable. Proposed tasks, planned tasks, etc. must be distinct instances.

In most cases, Tasks will have an intent of "order".

Distinguishes whether the task is a proposal, plan or full order.

STU3: Task.meta additional types (Meta) additional types from child elements (lastUpdated, profile, security, tag, versionId)

Element Task.meta is mapped to FHIR R4B element Task.meta as SourceIsBroaderThanTarget. The mappings for Task.meta do not cover the following types: Meta. The mappings for Task.meta do not cover the following types based on type expansion: lastUpdated, profile, security, tag, versionId.

STU3: Task.text additional types (Narrative) additional types from child elements (div, status)

Element Task.text is mapped to FHIR R4B element Task.text as SourceIsBroaderThanTarget. The mappings for Task.text do not cover the following types: Narrative. The mappings for Task.text do not cover the following types based on type expansion: div, status. Contained resources do not have narrative. Resources that are not contained SHOULD have a narrative. In some cases, a resource may only have text with little or no additional discrete data (as long as all minOccurs=1 elements are satisfied). This may be necessary for data from legacy systems where information is captured as a "text blob" or where text is additionally entered raw or narrated and encoded in formation is added later.

STU3: Task.definition[x] (new:Reference(ActivityDefinition), uri)

Element Task.definition[x] has a context of Task based on following the parent source element upwards and mapping to Task. Element Task.definition[x] has no mapping targets in FHIR R4B. Typically, this is because the element has been added (is a new element).

STU3: Task.identifier additional types (Identifier) additional types from child elements (assigner, period, system, type, use, value)

Element Task.identifier is mapped to FHIR R4B element Task.identifier as SourceIsBroaderThanTarget. The mappings for Task.identifier do not cover the following types: Identifier. The mappings for Task.identifier do not cover the following types based on type expansion: assigner, period, system, type, use, value.

STU3: Task.basedOn additional types from child elements (display, identifier, reference)

Element Task.basedOn is mapped to FHIR R4B element Task.basedOn as SourceIsBroaderThanTarget. The mappings for Task.basedOn do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.basedOn with unmapped reference targets: Resource.

STU3: Task.groupIdentifier additional types (Identifier) additional types from child elements (assigner, period, system, type, use, value)

Element Task.groupIdentifier is mapped to FHIR R4B element Task.groupIdentifier as SourceIsBroaderThanTarget. The mappings for Task.groupIdentifier do not cover the following types: Identifier. The mappings for Task.groupIdentifier do not cover the following types based on type expansion: assigner, period, system, type, use, value.

STU3: Task.partOf additional types from child elements (display, identifier, reference)

Element Task.partOf is mapped to FHIR R4B element Task.partOf as SourceIsBroaderThanTarget. The mappings for Task.partOf do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.partOf with unmapped reference targets: Task. This should usually be 0..1.

STU3: Task.focus additional types from child elements (display, identifier, reference)

Element Task.focus is mapped to FHIR R4B element Task.focus as SourceIsBroaderThanTarget. The mappings for Task.focus do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.focus with unmapped reference targets: Resource. If multiple resources need to be manipulated, use sub-tasks. (This ensures that status can be tracked independently for each referenced resource.).

STU3: Task.for additional types from child elements (display, identifier, reference)

Element Task.for is mapped to FHIR R4B element Task.for as SourceIsBroaderThanTarget. The mappings for Task.for do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.for with unmapped reference targets: Resource.

STU3: Task.context additional types from child elements (display, identifier, reference)

Element Task.context is mapped to FHIR R4B element Task.encounter as SourceIsBroaderThanTarget. The mappings for Task.context do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.context with unmapped reference targets: Encounter, EpisodeOfCare.

STU3: Task.executionPeriod additional types (Period) additional types from child elements (end, start)

Element Task.executionPeriod is mapped to FHIR R4B element Task.executionPeriod as SourceIsBroaderThanTarget. The mappings for Task.executionPeriod do not cover the following types: Period. The mappings for Task.executionPeriod do not cover the following types based on type expansion: end, start.

STU3: Task.requester.agent

Element Task.requester.agent is mapped to FHIR R4B element Task.requester as SourceIsBroaderThanTarget. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.requester.agent with unmapped reference targets: Device, Organization, Patient, Practitioner, RelatedPerson.

STU3: Task.requester.onBehalfOf (new:Reference(Organization))

Element Task.requester.onBehalfOf has a context of Task.requester based on following the parent source element upwards and mapping to Task. Element Task.requester.onBehalfOf has no mapping targets in FHIR R4B. Typically, this is because the element has been added (is a new element).

STU3: Task.owner

Element Task.owner is mapped to FHIR R4B element Task.owner as SourceIsBroaderThanTarget. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.owner with unmapped reference targets: Device, Organization, Patient, Practitioner, RelatedPerson. Tasks may be created with an owner not yet identified.

STU3: Task.note additional types (Annotation) additional types from child elements (author[x], text, time)

Element Task.note is mapped to FHIR R4B element Task.note as SourceIsBroaderThanTarget. The mappings for Task.note do not cover the following types: Annotation. The mappings for Task.note do not cover the following types based on type expansion: author[x], text, time.

STU3: Task.relevantHistory additional types from child elements (display, identifier, reference)

Element Task.relevantHistory is mapped to FHIR R4B element Task.relevantHistory as SourceIsBroaderThanTarget. The mappings for Task.relevantHistory do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.relevantHistory with unmapped reference targets: Provenance. This element does not point to the Provenance associated with the current version of the resource - as it would be created after this version existed. The Provenance for the current version can be retrieved with a _revinclude.

STU3: Task.restriction.period additional types (Period) additional types from child elements (end, start)

Element Task.restriction.period is mapped to FHIR R4B element Task.restriction.period as SourceIsBroaderThanTarget. The mappings for Task.restriction.period do not cover the following types: Period. The mappings for Task.restriction.period do not cover the following types based on type expansion: end, start. Note that period.high is the due date representing the time by which the task should be completed.

STU3: Task.restriction.recipient

Element Task.restriction.recipient is mapped to FHIR R4B element Task.restriction.recipient as SourceIsBroaderThanTarget. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.restriction.recipient with unmapped reference targets: Group, Organization, Patient, Practitioner, RelatedPerson.

STU3: Task.input.value[x] additional types (Address, Annotation, Attachment, ContactPoint, HumanName, Identifier, Period, Range, Ratio, SampledData, Signature, Timing, Meta)

Element Task.input.value[x] is mapped to FHIR R4B element Task.input.value[x] as RelatedTo. The mappings for Task.input.value[x] do not cover the following types: Address, Annotation, Attachment, ContactPoint, HumanName, Identifier, Meta, Period, Range, Ratio, SampledData, Signature, Timing. The target context Task.input.value[x] is a choice-type element and cannot directly hold extensions. The context is moved up to parent element Task.input.

STU3: Task.output.value[x] additional types (Address, Annotation, Attachment, ContactPoint, HumanName, Identifier, Period, Range, Ratio, SampledData, Signature, Timing, Meta)

Element Task.output.value[x] is mapped to FHIR R4B element Task.output.value[x] as RelatedTo. The mappings for Task.output.value[x] do not cover the following types: Address, Annotation, Attachment, ContactPoint, HumanName, Identifier, Meta, Period, Range, Ratio, SampledData, Signature, Timing. The target context Task.output.value[x] is a choice-type element and cannot directly hold extensions. The context is moved up to parent element Task.output.

A task to be performed.

The logical id of the resource, as used in the URL for the resource. Once assigned, this value never changes.

The only time that a resource does not have an id is when it is being submitted to the server using a create operation.

The metadata about the resource. This is content that is maintained by the infrastructure. Changes to the content might not always be associated with version changes to the resource.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.meta additional types (Meta) additional types from child elements (lastUpdated, profile, security, tag, versionId)

Element Task.meta is mapped to FHIR R4B element Task.meta as SourceIsBroaderThanTarget. The mappings for Task.meta do not cover the following types: Meta. The mappings for Task.meta do not cover the following types based on type expansion: lastUpdated, profile, security, tag, versionId.

The version specific identifier, as it appears in the version portion of the URL. This value changes when the resource is created, updated, or deleted.

The server assigns this value, and ignores what the client specifies, except in the case that the server is imposing version integrity on updates/deletes.

When the resource last changed - e.g. when the version changed.

This value is always populated except when the resource is first being created. The server / resource manager sets this value; what a client provides is irrelevant. This is equivalent to the HTTP Last-Modified and SHOULD have the same value on a read interaction.

A uri that identifies the source system of the resource. This provides a minimal amount of Provenance information that can be used to track or differentiate the source of information in the resource. The source may identify another FHIR server, document, message, database, etc.

In the provenance resource, this corresponds to Provenance.entity.what[x]. The exact use of the source (and the implied Provenance.entity.role) is left to implementer discretion. Only one nominated source is allowed; for additional provenance details, a full Provenance resource should be used.

This element can be used to indicate where the current master source of a resource that has a canonical URL if the resource is no longer hosted at the canonical URL.

A list of profiles (references to StructureDefinition resources) that this resource claims to conform to. The URL is a reference to StructureDefinition.url.

It is up to the server and/or other infrastructure of policy to determine whether/how these claims are verified and/or updated over time. The list of profile URLs is a set.

Security labels applied to this resource. These tags connect specific resources to the overall security policy and infrastructure.

The security labels can be updated without changing the stated version of the resource. The list of security labels is a set. Uniqueness is based the system/code, and version and display are ignored.

Tags applied to this resource. Tags are intended to be used to identify and relate resources to process and workflow, and applications are not required to consider the tags when interpreting the meaning of a resource.

The tags can be updated without changing the stated version of the resource. The list of tags is a set. Uniqueness is based the system/code, and version and display are ignored.

A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content. Often, this is a reference to an implementation guide that defines the special rules along with other profiles etc.

Asserting this rule set restricts the content to be only understood by a limited set of trading partners. This inherently limits the usefulness of the data in the long term. However, the existing health eco-system is highly fractured, and not yet ready to define, collect, and exchange data in a generally computable sense. Wherever possible, implementers and/or specification writers should avoid using this element. Often, when used, the URL is a reference to an implementation guide that defines these special rules as part of it's narrative along with other profiles, value sets, etc.

The base language in which the resource is written.

Language is provided to support indexing and accessibility (typically, services such as text to speech use the language tag). The html language tag in the narrative applies to the narrative. The language tag on the resource may be used to specify the language of other presentations generated from the data in the resource. Not all the content has to be in the base language. The Resource.language should not be assumed to apply to the narrative automatically. If a language is specified, it should it also be specified on the div element in the html (see rules in HTML5 for information about the relationship between xml:lang and the html lang attribute).

IETF language tag

A human-readable narrative that contains a summary of the resource and can be used to represent the content of the resource to a human. The narrative need not encode all the structured data, but is required to contain sufficient detail to make it "clinically safe" for a human to just read the narrative. Resource definitions may define what content should be represented in the narrative to ensure clinical safety.

Contained resources do not have narrative. Resources that are not contained SHOULD have a narrative. In some cases, a resource may only have text with little or no additional discrete data (as long as all minOccurs=1 elements are satisfied). This may be necessary for data from legacy systems where information is captured as a "text blob" or where text is additionally entered raw or narrated and encoded information is added later.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.text additional types (Narrative) additional types from child elements (div, status)

Element Task.text is mapped to FHIR R4B element Task.text as SourceIsBroaderThanTarget. The mappings for Task.text do not cover the following types: Narrative. The mappings for Task.text do not cover the following types based on type expansion: div, status. Contained resources do not have narrative. Resources that are not contained SHOULD have a narrative. In some cases, a resource may only have text with little or no additional discrete data (as long as all minOccurs=1 elements are satisfied). This may be necessary for data from legacy systems where information is captured as a "text blob" or where text is additionally entered raw or narrated and encoded in formation is added later.

The status of the narrative - whether it's entirely generated (from just the defined data or the extensions too), or whether a human authored it and it may contain additional data.

The actual narrative content, a stripped down version of XHTML.

The contents of the html element are an XHTML fragment containing only the basic html formatting elements described in chapters 7-11 and 15 of the HTML 4.0 standard, <a> elements (either name or href), images and internally contained stylesheets. The XHTML content SHALL NOT contain a head, a body, external stylesheet references, scripts, forms, base/link/xlink, frames, iframes and objects.

These resources do not have an independent existence apart from the resource that contains them - they cannot be identified independently, and nor can they have their own independent transaction scope.

This should never be done when the content can be identified properly, as once identification is lost, it is extremely difficult (and context dependent) to restore it again. Contained resources may have profiles and tags In their meta elements, but SHALL NOT have security labels.

An Extension

STU3: Task.definition[x] (new:Reference(ActivityDefinition), uri)

Element Task.definition[x] has a context of Task based on following the parent source element upwards and mapping to Task. Element Task.definition[x] has no mapping targets in FHIR R4B. Typically, this is because the element has been added (is a new element).

May be used to represent additional information that is not part of the basic definition of the resource and that modifies the understanding of the element that contains it and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. 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 is allowed to define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.

Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

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.

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

The business identifier for this task.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.identifier additional types (Identifier) additional types from child elements (assigner, period, system, type, use, value)

Element Task.identifier is mapped to FHIR R4B element Task.identifier as SourceIsBroaderThanTarget. The mappings for Task.identifier do not cover the following types: Identifier. The mappings for Task.identifier do not cover the following types based on type expansion: assigner, period, system, type, use, value.

The purpose of this identifier.

Applications can assume that an identifier is permanent unless it explicitly says that it is temporary.

Allows the appropriate identifier for a particular context of use to be selected from among a set of identifiers.

A coded type for the identifier that can be used to determine which identifier to use for a specific purpose.

This element deals only with general categories of identifiers. It SHOULD not be used for codes that correspond 1..1 with the Identifier.system. Some identifiers may fall into multiple categories due to common usage. Where the system is known, a type is unnecessary because the type is always part of the system definition. However systems often need to handle identifiers where the system is not known. There is not a 1:1 relationship between type and system, since many different systems have the same type.

Allows users to make use of identifiers when the identifier system is not known.

Establishes the namespace for the value - that is, a URL that describes a set values that are unique.

Identifier.system is always case sensitive.

There are many sets of identifiers. To perform matching of two identifiers, we need to know what set we're dealing with. The system identifies a particular set of unique identifiers.

The portion of the identifier typically relevant to the user and which is unique within the context of the system.

If the value is a full URI, then the system SHALL be urn:ietf:rfc:3986. The value's primary purpose is computational mapping. As a result, it may be normalized for comparison purposes (e.g. removing non-significant whitespace, dashes, etc.) A value formatted for human display can be conveyed using the Rendered Value extension. Identifier.value is to be treated as case sensitive unless knowledge of the Identifier.system allows the processer to be confident that non-case-sensitive processing is safe.

Time period during which identifier is/was valid for use.

Organization that issued/manages the identifier.

The Identifier.assigner may omit the .reference element and only contain a .display element reflecting the name or other textual information about the assigning organization.

The URL pointing to a FHIR-defined protocol, guideline, orderset or other definition that is adhered to in whole or in part by this Task.

Enables a formal definition of how he task is to be performed, enabling automation.

The URL pointing to an externally maintained protocol, guideline, orderset or other definition that is adhered to in whole or in part by this Task.

Enables a formal definition of how he task is to be performed (e.g. using BPMN, BPEL, XPDL or other formal notation to be associated with a task), enabling automation.

BasedOn refers to a higher-level authorization that triggered the creation of the task. It references a "request" resource such as a ServiceRequest, MedicationRequest, ServiceRequest, CarePlan, etc. which is distinct from the "request" resource the task is seeking to fulfill. This latter resource is referenced by FocusOn. For example, based on a ServiceRequest (= BasedOn), a task is created to fulfill a procedureRequest ( = FocusOn ) to collect a specimen from a patient.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.basedOn additional types from child elements (display, identifier, reference)

Element Task.basedOn is mapped to FHIR R4B element Task.basedOn as SourceIsBroaderThanTarget. The mappings for Task.basedOn do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.basedOn with unmapped reference targets: Resource.

A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

Plain text narrative that identifies the resource in addition to the resource reference.

This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

An identifier that links together multiple tasks and other requests that were created in the same context.

Billing and/or reporting can be linked to whether multiple requests were created as a single unit.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.groupIdentifier additional types (Identifier) additional types from child elements (assigner, period, system, type, use, value)

Element Task.groupIdentifier is mapped to FHIR R4B element Task.groupIdentifier as SourceIsBroaderThanTarget. The mappings for Task.groupIdentifier do not cover the following types: Identifier. The mappings for Task.groupIdentifier do not cover the following types based on type expansion: assigner, period, system, type, use, value.

The purpose of this identifier.

Applications can assume that an identifier is permanent unless it explicitly says that it is temporary.

Allows the appropriate identifier for a particular context of use to be selected from among a set of identifiers.

A coded type for the identifier that can be used to determine which identifier to use for a specific purpose.

This element deals only with general categories of identifiers. It SHOULD not be used for codes that correspond 1..1 with the Identifier.system. Some identifiers may fall into multiple categories due to common usage. Where the system is known, a type is unnecessary because the type is always part of the system definition. However systems often need to handle identifiers where the system is not known. There is not a 1:1 relationship between type and system, since many different systems have the same type.

Allows users to make use of identifiers when the identifier system is not known.

Establishes the namespace for the value - that is, a URL that describes a set values that are unique.

Identifier.system is always case sensitive.

There are many sets of identifiers. To perform matching of two identifiers, we need to know what set we're dealing with. The system identifies a particular set of unique identifiers.

The portion of the identifier typically relevant to the user and which is unique within the context of the system.

If the value is a full URI, then the system SHALL be urn:ietf:rfc:3986. The value's primary purpose is computational mapping. As a result, it may be normalized for comparison purposes (e.g. removing non-significant whitespace, dashes, etc.) A value formatted for human display can be conveyed using the Rendered Value extension. Identifier.value is to be treated as case sensitive unless knowledge of the Identifier.system allows the processer to be confident that non-case-sensitive processing is safe.

Time period during which identifier is/was valid for use.

Organization that issued/manages the identifier.

The Identifier.assigner may omit the .reference element and only contain a .display element reflecting the name or other textual information about the assigning organization.

Task that this particular task is part of.

This should usually be 0..1.

Allows tasks to be broken down into sub-steps (and this division can occur independent of the original task).

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.partOf additional types from child elements (display, identifier, reference)

Element Task.partOf is mapped to FHIR R4B element Task.partOf as SourceIsBroaderThanTarget. The mappings for Task.partOf do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.partOf with unmapped reference targets: Task. This should usually be 0..1.

A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

Plain text narrative that identifies the resource in addition to the resource reference.

This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

The current status of the task.

The current status of the task.

These states enable coordination of task status with off-the-shelf workflow solutions that support automation of tasks.

An explanation as to why this task is held, failed, was refused, etc.

This applies to the current status. Look at the history of the task to see reasons for past statuses.

Codes to identify the reason for current status. These will typically be specific to a particular workflow.

Contains business-specific nuances of the business state.

The domain-specific business-contextual sub-state of the task. For example: "Blood drawn", "IV inserted", "Awaiting physician signature", etc.

There's often a need to track substates of a task - this is often variable by specific workflow implementation.

Indicates the "level" of actionability associated with the Task, i.e. i+R[9]Cs this a proposed task, a planned task, an actionable task, etc.

This element is immutable. Proposed tasks, planned tasks, etc. must be distinct instances.

In most cases, Tasks will have an intent of "order".

Distinguishes whether the task is a proposal, plan or full order.

Indicates how quickly the Task should be addressed with respect to other requests.

The priority of a task (may affect service level applied to the task).

Used to identify the service level expected while performing a task.

A name or code (or both) briefly describing what the task involves.

The title (eg "My Tasks", "Outstanding Tasks for Patient X") should go into the code.

Codes to identify what the task involves. These will typically be specific to a particular workflow.

A free-text description of what is to be performed.

The request being actioned or the resource being manipulated by this task.

If multiple resources need to be manipulated, use sub-tasks. (This ensures that status can be tracked independently for each referenced resource.).

Used to identify the thing to be done.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.focus additional types from child elements (display, identifier, reference)

Element Task.focus is mapped to FHIR R4B element Task.focus as SourceIsBroaderThanTarget. The mappings for Task.focus do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.focus with unmapped reference targets: Resource. If multiple resources need to be manipulated, use sub-tasks. (This ensures that status can be tracked independently for each referenced resource.).

A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

Plain text narrative that identifies the resource in addition to the resource reference.

This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

The entity who benefits from the performance of the service specified in the task (e.g., the patient).

Used to track tasks outstanding for a beneficiary. Do not use to track the task owner or creator (see owner and creator respectively). This can also affect access control.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.for additional types from child elements (display, identifier, reference)

Element Task.for is mapped to FHIR R4B element Task.for as SourceIsBroaderThanTarget. The mappings for Task.for do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.for with unmapped reference targets: Resource.

A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

Plain text narrative that identifies the resource in addition to the resource reference.

This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

The healthcare event (e.g. a patient and healthcare provider interaction) during which this task was created.

For some tasks it may be important to know the link between the encounter the task originated within.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.context additional types from child elements (display, identifier, reference)

Element Task.context is mapped to FHIR R4B element Task.encounter as SourceIsBroaderThanTarget. The mappings for Task.context do not cover the following types based on type expansion: display, identifier, reference. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.context with unmapped reference targets: Encounter, EpisodeOfCare.

A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

Plain text narrative that identifies the resource in addition to the resource reference.

This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

Identifies the time action was first taken against the task (start) and/or the time final action was taken against the task prior to marking it as completed (end).

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.executionPeriod additional types (Period) additional types from child elements (end, start)

Element Task.executionPeriod is mapped to FHIR R4B element Task.executionPeriod as SourceIsBroaderThanTarget. The mappings for Task.executionPeriod do not cover the following types: Period. The mappings for Task.executionPeriod do not cover the following types based on type expansion: end, start.

The start of the period. The boundary is inclusive.

If the low element is missing, the meaning is that the low boundary is not known.

The end of the period. If the end of the period is missing, it means no end was known or planned at the time the instance was created. The start may be in the past, and the end date in the future, which means that period is expected/planned to end at that time.

The high value includes any matching date/time. i.e. 2012-02-03T10:00:00 is in a period that has an end value of 2012-02-03.

The date and time this task was created.

Most often used along with lastUpdated to track duration of task to supporting monitoring and management.

The date and time of last modification to this task.

Used along with history to track task activity and time in a particular task state. This enables monitoring and management.

The creator of the task.

Identifies who created this task. May be used by access control mechanisms (e.g., to ensure that only the creator can cancel a task).

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.requester.agent

Element Task.requester.agent is mapped to FHIR R4B element Task.requester as SourceIsBroaderThanTarget. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.requester.agent with unmapped reference targets: Device, Organization, Patient, Practitioner, RelatedPerson.

STU3: Task.requester.onBehalfOf (new:Reference(Organization))

Element Task.requester.onBehalfOf has a context of Task.requester based on following the parent source element upwards and mapping to Task. Element Task.requester.onBehalfOf has no mapping targets in FHIR R4B. Typically, this is because the element has been added (is a new element).

A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

Plain text narrative that identifies the resource in addition to the resource reference.

This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

The kind of participant that should perform the task.

The type(s) of task performers allowed.

Use to distinguish tasks on different activity queues.

Individual organization or Device currently responsible for task execution.

Tasks may be created with an owner not yet identified.

Identifies who is expected to perform this task.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

An Extension

STU3: Task.owner

Element Task.owner is mapped to FHIR R4B element Task.owner as SourceIsBroaderThanTarget. The standard extension alternate-reference has been mapped as the representation of FHIR STU3 element Task.owner with unmapped reference targets: Device, Organization, Patient, Practitioner, RelatedPerson. Tasks may be created with an owner not yet identified.

A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

Plain text narrative that identifies the resource in addition to the resource reference.

This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

Principal physical location where the this task is performed.