When using topic-based subscriptions, the primary criteria is always the topic, indicated by its canonical URL.

• value @ url

Search-style filters to be applied to narrow the subscription topic stream. Keys can be either search parameters appropriate to the filtering resource or keys defined within the subscription topic.

When multiple filters are applied, evaluates to true if all the conditions are met; otherwise it returns false. (i.e., logical AND).

• value @ url

If present, a 'hearbeat' notification (keepalive) is sent via this channel with an the interval period equal to this elements integer value in seconds. If not present, a heartbeat notification is not sent.

If present, the maximum amount of time a server will allow before failing a notification attempt.

If present, the maximum number of triggering resources that will be included in a notification bundle (e.g., a server will not include more than this number of trigger resources in a single notification). Note that this is not a strict limit on the number of entries in a bundle, as dependent resources can be included.

• value @ url

The type of channel to send notifications on.

This extension allows for the use of additional channel types that were not defined in the FHIR R4 subscription definition.

• value @ url

How much of the resource content to deliver in the notification payload. The choices are an empty payload, only the resource id, or the full resource content.

Sending the payload has obvious security implications. The server is responsible for ensuring that the content is appropriately secured.

When using topic-based subscriptions, the primary criteria is always the topic, indicated by its canonical URL.

An Extension

• value @ url

Search-style filters to be applied to narrow the subscription topic stream. Keys can be either search parameters appropriate to the filtering resource or keys defined within the subscription topic.

When multiple filters are applied, evaluates to true if all the conditions are met; otherwise it returns false. (i.e., logical AND).

An Extension

• value @ url

If present, a 'hearbeat' notification (keepalive) is sent via this channel with an the interval period equal to this elements integer value in seconds. If not present, a heartbeat notification is not sent.

If present, the maximum amount of time a server will allow before failing a notification attempt.

If present, the maximum number of triggering resources that will be included in a notification bundle (e.g., a server will not include more than this number of trigger resources in a single notification). Note that this is not a strict limit on the number of entries in a bundle, as dependent resources can be included.

An Extension

• value @ url

The type of channel to send notifications on.

This extension allows for the use of additional channel types that were not defined in the FHIR R4 subscription definition.

An Extension

• value @ url

How much of the resource content to deliver in the notification payload. The choices are an empty payload, only the resource id, or the full resource content.

Sending the payload has obvious security implications. The server is responsible for ensuring that the content is appropriately secured.

The subscription resource is used to define a push-based subscription from a server to another system. Once a subscription is registered with the server, the server checks every resource that is created or updated, and if the resource matches the given criteria, it sends a message on the defined "channel" so that another system can take an appropriate action.

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.

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).

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.

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.

May be used to represent additional information that is not part of the basic definition of the resource. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

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.

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).

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.

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.

The status of the subscription, which marks the server state for managing the subscription.

A client can only submit subscription resources in the requested or off state. Only the server can move a subscription from requested to active, and then to error. Either the server or the client can turn a subscription off.

This element is labeled as a modifier because the status contains codes that mark the resource as not currently valid.

Contact details for a human to contact about the subscription. The primary use of this for system administrator troubleshooting.

The time for the server to turn the subscription off.

The server is permitted to deviate from this time but should observe it.

A description of why this subscription is defined.

When using topic-based subscriptions, the primary criteria is always the topic, indicated by its canonical URL.

The rules are search criteria (without the [base] part). Like Bundle.entry.request.url, it has no leading "/".

unique id for the element within a resource (for internal references)

An Extension

• value @ url

Search-style filters to be applied to narrow the subscription topic stream. Keys can be either search parameters appropriate to the filtering resource or keys defined within the subscription topic.

When multiple filters are applied, evaluates to true if all the conditions are met; otherwise it returns false. (i.e., logical AND).

The actual value

A record of the last error that occurred when the server processed a notification.

Details where to send notifications when resources are received that meet the criteria.

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

An Extension

• value @ url

If present, a 'hearbeat' notification (keepalive) is sent via this channel with an the interval period equal to this elements integer value in seconds. If not present, a heartbeat notification is not sent.

If present, the maximum amount of time a server will allow before failing a notification attempt.

If present, the maximum number of triggering resources that will be included in a notification bundle (e.g., a server will not include more than this number of trigger resources in a single notification). Note that this is not a strict limit on the number of entries in a bundle, as dependent resources can be included.

May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained 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 can 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).

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.

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.

The type of channel to send notifications on.

unique id for the element within a resource (for internal references)

An Extension

• value @ url

The type of channel to send notifications on.

This extension allows for the use of additional channel types that were not defined in the FHIR R4 subscription definition.

Primitive value for code

The url that describes the actual end-point to send messages to.

For rest-hook, and websocket, the end-point must be an http: or https: URL; for email, a mailto: url, for sms, a tel: url, and for message the endpoint can be in any form of url the server understands (usually, http: or mllp:). The URI is allowed to be relative; in which case, it is relative to the server end-point (since there may be more than one, clients should avoid using relative URIs).

The mime type to send the payload in - either application/fhir+xml, or application/fhir+json. If the payload is not present, then there is no payload in the notification, just a notification. The mime type "text/plain" may also be used for Email and SMS subscriptions.

Sending the payload has obvious security implications. The server is responsible for ensuring that the content is appropriately secured.

unique id for the element within a resource (for internal references)

An Extension

• value @ url

How much of the resource content to deliver in the notification payload. The choices are an empty payload, only the resource id, or the full resource content.

Sending the payload has obvious security implications. The server is responsible for ensuring that the content is appropriately secured.

Primitive value for code

Additional headers / information to send as part of the notification.

Exactly what these mean depend on the channel type. They can convey additional information to the recipient and/or meet security requirements; for example, support of multiple headers in the outgoing notifications for rest-hook type subscriptions.