Glossary

Audit trail. A record of who did what to which resource, and what was refused. It is read back as FHIR AuditEvent resources at GET /_audit, and its entries are chained with a hash so that tampering is detectable. See Governance.

Batch. A Bundle of type batch. Each entry is its own commit, so a subscriber can see a batch half applied. Compare transaction.

Commit. A write that has been validated and made durable. A commit is what wakes the live queries it could have changed.

Commit timestamp. A logical counter that rises with every commit, starting at 1. It is not a wall-clock time. Compare timestamps as numbers.

Live query. A subscription to the result of a query, over the /sync WebSocket. The server re-runs the query when a commit could have changed its answer, and pushes the new full result. Also called a reactive query. See How live queries work.

meta.versionId. The version of a resource. ReFHIR sets it to the commit timestamp of the write that produced that version, so it also orders versions. A mismatched If-Match is refused with a 409.

Operation. The name of what a live query or a /sync mutation runs, written {ResourceType}/{operation}, such as Patient/search or Patient/update. In the protocol it is the udfPath field.

Package. A FHIR package, such as hl7.fhir.r4.core, that supplies the resource types, search parameters and profiles a server knows. ReFHIR ships none and installs them on the first start.

Primary, standby, replica. The roles of several processes sharing one database. The primary writes and holds the lease. A standby waits for the lease and takes over when the primary is gone. A replica serves reads, and forwards writes to the primary. See Several processes.

Query-set version. A counter each /sync connection keeps, starting at 0. It is the only sequencing the protocol has, and it is about the set of live queries, not about the data.

Read-your-writes. The guarantee that a read after your own write sees it. ReFHIR’s REST reads that follow a write wait for a replica to catch up, using the X-Refhir-Commit-Ts and X-Refhir-Min-Ts headers. The TypeScript client tracks lastCommitTs for this.

Read set. What a query read while it ran: the index ranges it touched. A write wakes a live query when it overlaps the query’s read set.

Resource. A FHIR resource: a Patient, an Observation, a MedicationRequest.

SMART App Launch. The FHIR authorization framework. ReFHIR implements version 2.2 as both authorization server and resource server. See SMART on FHIR.

Snapshot. A consistent view of the data as of one commit timestamp. A read at timestamp t sees the newest version of each resource at or before t.

Subscription. The FHIR R4 resource that asks to be notified. ReFHIR delivers rest-hook and websocket Subscriptions. It is not the same as a live query. See Live queries and FHIR Subscriptions.

Transaction. A Bundle of type transaction. It commits at one timestamp or not at all, and a subscriber sees all of its effects on a query result or none of them.

Transition. The /sync message that carries results to a client. It holds QueryUpdated, QueryFailed and QueryRemoved items.

Watch. The client-side handle for one live query. In the TypeScript and Go clients, latest() returns the newest result and next() waits for a new one.