1. Scope

S1.1 Every port MUST support FHIR R5 (5.0.0), R4 (4.0.1), and R3 (3.0.2). R5 is the default everywhere a version is optional.
S1.2 Each FHIR version's data lives in its own namespace: r5, r4, r3. Versions are independent; a database MAY host any subset. The namespace is realized by whatever mechanism the engine provides for isolating a set of tables under a name, and the mechanism is a dialect concern (X15.6) — the requirement is that the three versions never share a table.
S1.3 All resource types defined by the version's specification MUST be supported — no unsupported-type errors for spec-defined types.
S1.4 Each port MUST declare a minimum engine version and MUST NOT silently work below it. Features requiring at least that version MAY be used; older servers are unsupported. The floor is a dialect decision because it is driven by dialect facts — an identifier length, a boolean type, a JSON type, a window function — and it MUST be stated in the port's annex rather than inherited by assumption.

Engine bindings#

Non-normative summary; each port's annex is authoritative for its own row.

Port	Engine	Declared floor	Namespace mechanism
`fhir-postgresql`	PostgreSQL	18	`CREATE SCHEMA r5`
`fhir-sqlite`	SQLite	3.35+	one database file, or `ATTACH` per version
`fhir-mysql`	MySQL	8.4	database (`CREATE DATABASE r5`)
`fhir-mariadb`	MariaDB	11.4	database (`CREATE DATABASE r5`)
`fhir-mssql`	SQL Server	2019+	`CREATE SCHEMA r5`
`fhir-oracle`	Oracle Database	12.2+, declared in `M14.2`	user/schema

Oracle's row was the open one: identifiers were 30 bytes before 12.2 and 128 after, so the generator's identifier budget (G2.4) is only safe on 12.2+. Closed — M14.2 declares the 12.2 floor and states the identifier fact that sets it, and M14.3 requires init to verify the server version and refuse below it (audit.md F-09).

Both halves are now measured rather than cited: on Oracle 26ai a 128-byte identifier creates and a 129-byte one fails with ORA-00972: ... exceeds the maximum length of 128 bytes, so the 63-byte budget is safe and conservative above the floor (M14.23b).

Out of scope#

Stated here so that "not implemented" and "not intended" are distinguishable:

Authentication and authorization in the library core. Identity is established at the deployment perimeter; §12 defines what the core records regardless.
Terminology services — $expand, $validate-code, code-system-aware validation beyond a value set's literal codes (§9).
A FHIRPath evaluation engine, subscriptions, and GraphQL.
Profile and implementation-guide validation beyond the base specification.
An HTTP service and a command-line tool (C0.15).

Part of the fhir-databases specification.