DSTU2 QA Preview

This page is part of the FHIR Specification (v1.0.0: DSTU 2 Ballot 3). The current version which supercedes this version is 5.0.0. For a full list of available versions, see the Directory of published versions

1.15.0 Compartment Based Access

FHIR Infrastructure Work GroupMaturity Level: 3Ballot Status: DSTU 2

1.15.0.1 Compartments

Each resource may belong to one or more logical compartments. A compartment is a logical grouping of resources which share a common property. Compartments have two principal roles:

  • Function as an access mechanism for finding a set of related resources quickly
  • Provide a definitional basis for applying access control to resources quickly

Compartment definitions describe how particular compartment instances are named and identified, and how systems know which resources are in the compartment. The following compartments are defined by this specification:

TitleDescriptionIdentityMembership
PatientThe set of resources associated with a particular patientThere is an instance of the patient compartment for each patient resource, and the identity of the compartment is the same as the patient. When a patient is linked to another patient, all the records associated with the linked patient are in the compartment associated with the target of the link.The patient compartment includes any resources where the subject of the resource is the patient, and some other resources that are directly linked to resources in the patient compartment
EncounterThe set of resources associated with a particular encounterThere is an instance of the encounter compartment for each encounter resource, and the identity of the compartment is the same as the encounterThe encounter compartment includes any resources where the resource has an explicitly nominated encounter, and some other resources that them selves link to resources in the encounter compartment. Note that for many resources, the exact nature of the link to encounter can be ambiguous (e.g. for a DiagnosticReport, is it the encounter when it was initiated, or when it was reported?)
RelatedPersonThe set of resources associated with a particular 'related person'There is an instance of the relatedPerson compartment for each relatedPerson resource, and the identity of the compartment is the same as the relatedPersonThe relatedPerson compartment includes any resources where the resource is explicitly linked to relatedPerson (usually as author)
PractitionerThe set of resources associated with a particular practitionerThere is an instance of the practitioner compartment for each Practitioner resource, and the identity of the compartment is the same as the PractitionerThe practitioner compartment includes any resources where the resource is explicitly linked to a Practitioner (usually as author, but other kinds of linkage exist)
DeviceThe set of resources associated with a particular deviceThere is an instance of the practitioner compartment for each Device resource, and the identity of the compartment is the same as the DeviceThe device compartment includes any resources where the resource is explicitly linked to a Device (mostly subject or performer)

Compartments are defined and added the list above when implementer communities identify them as common access points for data. As described below, compartments have both syntactical and logical consequences, and both these aspects of their functionality are evaluated when deciding whether to define compartments.

1.15.0.2 Using Compartments

As an example of compartment usage, to retrieve a list of a patient's conditions, use the URL: 

  GET [base]/Patient/[id]/Condition

Additional search parameters can be defined, such as this hypothetical search for acute conditions: 

  GET [base]/Patient/[id]/Condition?code:in=http://hspc.org/ValueSet/acute-concerns

Note that as searches, these are syntactic variations on these two search URLs respectively: 

  GET [base]/Condition?patient=[id]
  GET [base]/Condition?patient=[id]&code:in=http://hspc.org/ValueSet/acute-concerns

However, there is a key difference in functionality between compartment based searches and direct searches with parameters. Consider this search: 

  GET [base]/Patient/[id]/Communication

Because the definition of the patient compartment for Commnunication says that aCommunication resource is in the patient compartment if the subject, sender, or recipient is the patient, the compartment search is actually the same as the union of these 3 searches: 

  GET [base]/Condition?subject=[id]
  GET [base]/Condition?sender=[id]
  GET [base]/Condition?recipient=[id]

There is no way to do this as a single search, except by using the _filter: 

  GET [base]/Condition?_filter=subject re [id] or sender re [id] or recipient re [id]

Further details of searching by compartment are described under the search operation. As a search related operation, the assignment of resources to compartments is only based on the current version of any of the resources involved. Note that contained patient resources cannot create a patient compartment of their own.

Compartments may be used explicitly, like this, but can also be used implicitly. For instance, if a FHIR server is providing a patient view of a record, the authorized user associated with use of the FHIR RESTful API may be limited to accessing records from the compartment instance(s) logically associated with their identity. Irrespective of whether compartments are being used explicitly or implicitly, servers will need to make arrangements to make some resources with no direct link to a patient available to the client (medications, substances, etc.).

Note that resources may cross between compartments, or interlink them. Examples of this would be where a Diagnostic Report identifies a subject, but an Observation it references identifies a different subject, or where a List resource references items that identify different subjects. Such cross-linking may arise for many valid reasons, including:

  • Cases where subject records are inter-linked - Transplants, Perinatal care, family therapy etc.
  • Workflow management where action lists link multiple patients and/or practitioners

Given the wide variety of use cases and contexts in which FHIR is used, compartments do not define how cross-linking is handled. Systems may reject resources, remove them from both compartments, or place them in both, or act in some other fashion.

It is at the discretion of the server whether to include resources in a compartment when the reference to the resource that establishes the compartment is in an extension.

Some resources are not in any compartment, e.g. Medication, Substance, Location. These resources are not directly to a patient or authored record, and are some times called 'master files'. Servers will need to make arrangements to make these resources available to the clients that are limited to particular compartments. For example, a Medication resource describes a medication itself and does not link to a patient; however, a resource such as MedicationAdministration connects the Medication (details of what was administered) to the patient (for whom was it administered), and so is required to interpret the administration.