ifc-schema

IFC schema as data: entity table, supertype chain, attribute names.

Status	Implemented
Latest release	0.3.0 (2026-09-29)
Registries	crates.io ifc-schema
Via the facade	openbim-ifc feature properties, schema-api
API documentation	rustdoc · docs.rs
Source	crates/ifc-schema/

Overview

ifc-schema — the IFC schema as data, not as 2,500 generated structs.

Features

Feature	Default	Enables
artifact		dep:bincode, dep:thiserror
express		dep:openbim-step
generation		express, ifc2x3, ifc4, ifc4x1, ifc4x2, ifc4x3
ifc2x3	yes	artifact
ifc4	yes	artifact
ifc4x1	yes	artifact
ifc4x2	yes	artifact
ifc4x3	yes	artifact

Changes

Latest release, 0.3.0 (2026-09-29):

Changed (breaking)

• Artifact format 3 records the facts above; format 1 and 2 artifacts still decode, with those facts empty.
• A nested aggregate attribute's type_name is its innermost element type (IfcLengthMeasure for LIST OF LIST OF IfcLengthMeasure), where the old extractor recorded the inner keyword LIST.
• The express and generation features use openbim-step =0.10.0 (the runtime links none).
• One cargo feature per bundled release (#112): ifc2x3, ifc4, ifc4x1, ifc4x2 and ifc4x3, all in default, so a default build bundles every release as before. Each accessor (ifc2x3(), ifc4(), ...) exists only with its feature. ifc4 used to ship all bundled tables; it now ships IFC4 only, so a build with default-features = false, features = ["ifc4"] loses the other releases -- name them, or keep defaults.
• for_version returns Result<&Schema, NotBundled> instead of Option<&Schema>, and exists in every build. Err(NotBundled) means a recognised release whose feature is off; an unknown FILE_SCHEMA token is still None from SchemaVersion::from_header_token, so the two cases stay distinguishable.
• write_structural_catalog and write_direct_structural_catalog exist in every build and return an io::ErrorKind::Unsupported error wrapping NotBundled for a release that is not compiled in, instead of panicking.
• artifact_decode_schema and BundledSchemaError need the new artifact feature (enabled by every release feature) instead of ifc4.
• SchemaVersion is #[non_exhaustive], derives Hash, and gains Ifc4x1 and Ifc4x2 (#33). A match on it needs a wildcard arm; a consumer should refuse a release it has not verified, never alias it to a neighbour. write_structural_catalog and write_direct_structural_catalog accept the new versions.
• ifc-schema owns its schema types. Attribute, EntityDef, TypeDef, TypeKind and the newly exported WhereRule are defined here instead of re-exported from openbim_step::express, and all five are #[non_exhaustive]: construct them with Attribute::new, EntityDef::new, TypeDef::new, WhereRule::new and the builder methods (with_supertype, with_attribute, with_derived, with_where_rule, abstract_entity, optional, aggregate), and give every match on TypeKind a wildcard arm. Field names, supertype(), is_derived() and is_defined() are unchanged. Rationale: an openbim-step release no longer ripples into this crate's public API, and later facts about a declaration (aggregate bounds, INVERSE, UNIQUE) can be added as fields without another break.
• openbim-step is an optional dependency, linked only by the new express feature and by generation. The bundled tables decode straight into the owned types; the default build no longer links a parser.
• Schema::from_express and Schema::from_express_bytes require the new express feature.
• Removed: Schema::from_parsed(ParsedSchema) (use Schema::new(name, entities, types)), Schema::graph() (the openbim_step::SchemaGraph it returned is no longer held; Schema answers the same queries itself), and the express module with its parse/ParsedSchema re-exports (use openbim_step::express directly).
• EntityDef no longer carries redeclared/is_redeclared(). No bundled table ever recorded explicit redeclarations (the artifact format drops them), so they were always empty for ifc2x3(), ifc4() and ifc4x3().
• artifact_decode_schema returns a Schema and artifact_encode_schema (generation) takes one, instead of openbim_step::express::ParsedSchema.

Added

• Aggregate bounds, nested aggregation, INVERSE and UNIQUE (#111): Attribute::aggregation (levels outermost first, each an Aggregation with AggregateKind, lower and upper Bound, unique, optional_elements), EntityDef::inverses (InverseAttribute) and EntityDef::unique_rules (UniqueRule), with builders. Additive: the types were already #[non_exhaustive]. All five bundled tables are regenerated with them: 115/153/158/160/165 INVERSE and 17/4/4/4/4 UNIQUE declarations for IFC2X3/IFC4/IFC4X1/IFC4X2/IFC4X3, pinned by tests.
• NotBundled, SchemaVersion::is_bundled() and SchemaVersion::feature_name().
• IFC4X1 FINAL and IFC4X2 FINAL (#33): bundled tables data/ifc4x1-final.bin (801 entities, 400 types) and data/ifc4x2-final.bin (816 entities, 407 types), generated from the official EXPRESS files like the other three; accessors ifc4x1() and ifc4x2(); for_version returns them; header tokens IFC4X1 and IFC4X2 (the files' own SCHEMA names); release ids IFC4X1_FINAL and IFC4X2_FINAL. Tests pin that both counts differ from IFC4 and IFC4X3 and that each carries its own release's entities.
• SchemaVersion::ALL, every known version oldest first.
• Schema::new, Schema::entities() and Schema::types() (declarations in source order), PartialEq/Eq for Schema, and the BundledSchemaError export.

Unchanged

• The bundled artifacts are byte-identical: regenerating all three with the ported generator reproduces the committed files, and FORMAT_VERSION stays 2.

Changed

• Requires openbim-step 0.7.0, matching ifc-step. Both pin the parser exactly, so the pair must move together. openbim-step 0.6 replaced EntityDef::supertype (a field) with supertypes plus a supertype() accessor for multiple inheritance; IFC schemas are single-inheritance, so the serialized artifact is unchanged.

Full history: crates/ifc-schema/CHANGELOG.md