FHIR-XDS-terminology

This page is a repository for terminology issues. Many XDS developers will be confused by FHIR's use of terminology. Between XDS and FHIR there is overlapping terminology but the terms have different meanings. In other cases a newer technology/standard is used instead of the ones chosen for XDS and we describe how the choices relate.

Document

In FHIR a document is a structured/organized collection of resources. A document can be submitted. When received at the server it can be saved as a document OR broken apart into individual resources. This is a decision of the server. If the server keeps the document as a single entity then it can be retrieved as a single object (will have a permanent URI assigned). If the server saved it as individual resources then the individual resources can be retrieved individually (they will each have a permanent URI).

To fully appreciate this semantic you must realize that HL7 anticipates that FHIR will eventually replace V2, V3, and CDA. Maintaining a document as a single entity would mimic the behavior of the current CDA specification with one very large expansion of capability. Individual parts of a document can be web addressable (have their own URI). Again, a choice of the receiving server.

DocumentManifest

The FHIR equivalent to SubmissionSet.

DocumentReference

The FHIR equivalent to DocumentEntry.

Logical ID

A resource has a single identity which is the full URL which can be used to retrieve it through a REST interface.

This identity is:

<FHIR Server>/<Resource Type>/<Resource Logical ID>

There are two strategies for assigning Logical IDs. FHIR does not assume Logical IDs are globally unique since they only need to identify a resource on a single FHIR server. The combination of the FHIR server address combined with the locally unique Logical ID creates a unique identification. A FHIR server may, but is not required, to assign UUIDs as Logical IDs. UUIDs are globally unique. This allows the resource to be identified independent of the FHIR server that supplied it. While there are advantages to both approaches, the use of UUIDs for Logical IDs maps to the current XDS approach where entryUUIDs shall be UUIDs.

But, this gets complicated. In a recent message on the FHIR list, Grahame commented:

You should be careful about the resource id - it's a technical id, not a logical id. For instance, if the set of resources you are interested in gets copied to a different server, it might have to change the identities - but it would also have to update the references. So it works - this is just a note of caution about it. But most resources have logical identifiers as well as literal identifiers, and these are constant across various servers, and CDA / v2 etc

So, I am confused regarding the meaning of logical id and need to read further.

Metadata

Properties about a Resource that describes some aspects of how the Resource behaves. Metadata Properties are coded outside the Resource. In REST they are carried as HTTP headers and in ATOM they are carried as details coded in the Entry but outside the Resource.

In XDS, metadata is a collection of properties about a document. In FHIR metadata describes Resources (which from an XDS perspective are metadata).

Resource

The fundamental building block in FHIR is the resource. Two in particular are of interest to XDS, DocumentReference and DocumentManifest. DocumentReference maps to DocumentEntry and DocumentManifest maps to SubmissionSet. There is no FHIR equivalent to Folder.