Rendered from docs/obligations/0139-an-identifier-scheme-glues-three-parts-into-one-string-so-nothing-can-decide-that-two-schemes-are-disjoint.md in the Headwater corpus. Every document on this half of the site is typed by the taxonomy the descriptor names: corpus.json.

An identifier scheme glues three parts into one string, so nothing can decide that two schemes are disjoint

Context

HW-OBL-0046 has asked for this since 2026-08-12. It traces to spec 2 and spec 3, which say a grammar with separate fields makes disjointness decidable by construction.

Pull request #207 moved the namespace to the front of every identifier pattern and expanded literal_prefix to expand the declared namespace before comparing. That left the underlying grammar untouched, and the obligation stayed open.

engine/crates/meta/meta-schema.yml still declares identifier_scheme.pattern as one string holding the prefix, the namespace placeholder, and the local-part form together. Five places in the corpus name this gap, and none of them names a work item that owns it.

Obligation

The corpus owes a grammar for identifier_scheme that declares the prefix, the namespace, and the local-part form as separate members. Today pattern in the meta-schema carries all three glued into one string, and the engine cannot read the prefix it mints.

Template::parse(pattern, namespace) is the sole constructor that three production sites depend on. Those sites mint identifiers, generate the identifier.pattern.not_met finding, and read schemes during taxonomy audit. A grammar change is a constructor swap, because Template still exposes mint, admits, sequence_of, render, and needs unchanged.

Disjointness is undecidable from a pattern string, and headwater taxonomy validate reports as much on every run. literal_prefix in engine/crates/resolve/src/rules.rs expands the declared namespace, then compares only the text before the first placeholder left. That decides a pair of schemes only when the prefix sits in front of every free placeholder. Two schemes whose free placeholders meet each other remain undecided.

The same gap reaches identifier publication. engine/crates/generate/src/profile.rs declares seven emitters, and only json and jsonschema are built. rdf and skos parse and refuse, because Q13 gates each unbuilt format behind a named external consumer, and none exists. The OWL and SKOS worked example shows what an emitter does without a grammar. It mints an IRI from a file path, and a rename breaks every reference to it.

Discharge

Discharge requires identifier_scheme to declare the prefix, the namespace, and the local-part form as separate members, with the # gap: comment removed rather than reworded. Template must be built from those members, with Template::parse gone or kept only as a shim pinned by a test.

The existing tests in check/src/identifier.rs must still pass, and mint, admits, sequence_of, render, and needs must keep their current behavior. identifier_integrity must decide disjointness from declared prefixes, literal_prefix must be gone, and headwater taxonomy validate must not print a not-decided clause.

All nine schemes must declare the new members, .headwater/taxonomy.lock must regenerate, and every string mint produces must stay byte-identical to what it produces today. The taxonomy major version must bump, per the cost that HW-OBL-0046 states, and spec 2 and spec 3 must describe the new members.

HW-OBL-0046 reaches a terminal state naming this obligation, and this obligation waits on the grammar change landing.