# ifc-classification instructions
Purpose: Borrowed IFC4 classification, document, library, association, hierarchy,
and transaction-staged authoring semantics.
Follow `../AGENTS.md`. Read `PLAN.md` only for assigned implementation or
roadmap work; keep progress, blockers, and evidence there.
## Boundary
Allowed production dependencies: `ifc-model`, `ifc-schema`, and shared error
support only. Views borrow the model. Authoring stages edits on a caller-owned
`ifc_model::Transaction`; this crate does not own commit or rollback.
The implemented boundary is ten concrete IFC4 records: classification,
classification reference, document information/reference, library
information/reference, the three `IfcRelAssociates*` families, and
`IfcExternalReferenceRelationship`. Approval and constraint resources remain
separate sibling domains.
## Module ownership
- `view.rs`: strict shared scalar/reference decoding and `ClassificationView`
- `classification.rs`: systems, editions, and hierarchical references
- `document.rs`: document information/references
- `library.rs`: library information/references
- `assignment.rs`: classification/document/library object associations
- `external_relationship.rs`: generic external-reference resource relationships
- `query.rs`: bounded hierarchy and explicit occurrence/type lookup
- `authoring.rs`: transaction-staged creation and pre-staging validation
- `error.rs`: malformed, unresolved, ambiguous, budget, and authoring failures
## Invariants
- External URI/file/network access is never triggered by reading a view.
- Classification codes are identifiers, not numbers; preserve formatting and hierarchy.
- Occurrence and type associations are returned separately and never silently merged.
- Missing, malformed, dangling, wrong-kind, cyclic, ambiguous, or budget-exhausted input returns a typed failure.
- Interpreted inherited-first slot layouts are pinned against bundled IFC4 metadata.
- Authoring validates the complete draft before its first staged edit.
- Iteration and relationship query output is deterministic by entity ID.
Keep entity views, relationship traversal, mutation, and domain algorithms in
separate files. Public exports flow through `lib.rs` deliberately.
## Verification
Run `cargo +1.88.0 test -p ifc-classification`, strict all-target clippy, the
classification mutation harness, then the package architecture/context/full
gates. Relationship changes require cycle, dangling, wrong-type, ambiguity,
budget, and rollback cases as applicable.