2. Identifiers

Requirement prefix: I2.

Identifiers are how openEHR names records, versions, archetypes, and terminologies. They are exchanged as text, compared as text, and appear in every REST path and every reference, so the rules about what text is accepted and what text is produced are load-bearing rather than cosmetic.

Parsing#

• I2.1 Every identifier type MUST be parsed into its parts at the boundary, not held as an opaque string. An unparsed OBJECT_VERSION_ID makes preceding_version_uid unverifiable, which is what lets a client commit a version whose parent belongs to a different versioned object.
• I2.2 A parsed identifier MUST print back to exactly the text it was parsed from, except where a requirement below explicitly normalises.
• I2.3 Input that would not survive I2.2 MUST be refused rather than normalised.

Primitive UIDs#

• I2.4 UID MUST be resolved to one of UUID, ISO_OID, or INTERNET_ID by lexical shape, tried in that order.
• I2.5 ISO_OID MUST be tried before INTERNET_ID, because an all-digit dotted string satisfies both grammars and openEHR uses OIDs for issuing authorities.
• I2.6 UUID MUST be five hexadecimal groups of lengths 8-4-4-4-12.
• I2.7 UUID equality and hashing MUST be case-insensitive, and the stored text MUST keep the case it was given. Normalising case would change an identifier that a caller round-trips; comparing case-sensitively would fail to find a record keyed under the other case.
• I2.8 ISO_OID arcs MUST be non-empty and all digits.
• I2.9 INTERNET_ID labels MUST be non-empty, MUST consist of [A-Za-z0-9_-], and MUST NOT begin or end with a separator.

OBJECT_ID descendants#

• I2.10 HIER_OBJECT_ID MUST parse as uid [ '::' extension ]. The extension MUST be non-empty when present and MUST NOT contain ::, because either would make the printed form re-parse into different parts.
• I2.11 OBJECT_VERSION_ID MUST parse as exactly three ::-separated parts: object_id, creating_system_id, version_tree_id.
• I2.12 VERSION_TREE_ID MUST parse as trunk or trunk.branch_number.branch_version, every component a positive integer.
• I2.13 VERSION_TREE_ID MUST refuse a leading zero. 01 and 1 denote one version, and accepting both would make two distinct strings name it.
• I2.14 ARCHETYPE_ID MUST parse as rm_originator '-' rm_name '-' rm_entity '.' domain_concept '.' version, with the domain concept containing no ..
• I2.15 ARCHETYPE_ID MUST accept a version of one, two, or three numeric components after the v. This departs from the BASE grammar, which gives one; ADL 2 archetypes carry three and the CKM publishes both, so the narrower grammar would reject identifiers that appear in real instance data. The guarantee that survives: the major version is always extractable, and the text round-trips (I2.2).
• I2.16 TEMPLATE_ID MUST be non-empty and free of whitespace. openEHR gives its lexical form as "to be determined"; inventing a stricter grammar would reject valid identifiers from conformant tools, and accepting anything would let a missing template id look present.
• I2.17 TERMINOLOGY_ID MUST parse as name [ '(' version ')' ] with both parts non-empty when present.
• I2.18 GENERIC_ID MUST require both value and scheme to be non-empty, so that an identifier in an uncontrolled scheme at least says which scheme.
• I2.19 UID_BASED_ID MUST admit only HIER_OBJECT_ID and OBJECT_VERSION_ID, as openEHR's typing of LOCATABLE.uid requires.
• I2.20 Where _type is absent, OBJECT_ID MUST be inferred only between HIER_OBJECT_ID and OBJECT_VERSION_ID, by counting :: separators. It MUST NOT guess ARCHETYPE_ID, TEMPLATE_ID, or GENERIC_ID, which are not distinguishable by shape.

References#

• I2.21 OBJECT_REF namespaces MUST match [a-zA-Z][a-zA-Z0-9_.:/&?=+-]*.
• I2.22 local and unknown MUST remain distinguishable: local asserts this system's identifier space, unknown records that the space was never captured. Collapsing them turns missing provenance into a claim of provenance.
• I2.23 PARTY_REF.type MUST be one of PERSON, ORGANISATION, GROUP, AGENT, ROLE, PARTY, ACTOR, or ANY, enforced at construction rather than at validation. A PARTY_REF naming a clinical class is a call that should not have compiled.
• I2.24 LOCATABLE_REF.path MUST be absent rather than empty to denote the root object, and the two MUST NOT both be representable.
• I2.25 LOCATABLE_REF MUST render as the URI namespace ':' id [ '/' path ] without doubling a separator when the path already begins with /.