A kind of building object BuildPlan can classify, specify, and eventually build. Aggregate root; Airtable object_classes. Answers "what kind of thing is this?" — not a product, a model, or a Revit category.

The single-parent ancestry between object classes (ADR-0046). At most one parent per class, acyclic. This is the edge set only; parameter inheritance is a separate concept that reads it.

The parentless ancestor at the top of a class's lineage. Derived and persisted on each row. Explicitly NOT an input to Revit category resolution — that was a DAG-era rule retired with ADR-0046.

Uniformat, Masterformat, OmniClass, and ObjectClass codes cross-referenced from a class. The first three plus Revit category use inherit-by-default fill with make-unique (ADR-0050); OmniClass is a flat non-propagating link.

ADR-0050 fill rule. Stewards author *_direct only; make-unique is inferred on edit. The value fills down from the nearest make-unique ancestor until the next one. Effective mirrors materialized *_direct, so no read-time walk happens.

The single Revit category an object class classifies as (0..1), with health status current | stale | needs_review | unresolved and provenance authored | inherited. Distinct from Revit category scope — this classifies a class, that describes a parameter binding's coverage.

The canonical identity and meaning of one parameter, independent of where it is used or how it is rendered. Aggregate root; Airtable parameter_keys; REST /parameter-keys. Owned by bim-ontology, consumed by product-marketplace (ADR-0006).

draft → active → approved → archived, invariant-checked. ParameterKey is the only aggregate with active. See the "Why active exists" section below — it is the scraping contract, not an extra step.

Which product contexts a key participates in — variant_option, product_spec, bim_parameter, mfg_takeoff, qto_takeoff. Non-empty set. bim_parameter membership is load-bearing - it gates automatic Revit projection. Not the same as Revit document altitude.

The value semantics of a key — what kind of value, whether measurable, which unit system. BuildPlan's own semantics, mapped onto an Autodesk RevitSpecType. Airtable parameter_specs.

How a parameter is presented for authoring or selection. Constrains the interaction where ParameterSpec constrains the value. Airtable parameter_controls.

The authoring grouping that organizes related keys for humans. The source both Revit group projections derive from; not itself a Revit artifact.

One canonical value a key can take, optionally carrying measured quantities. Quantity roles distinguish primary, alternate, min, max, and modifier readings.

A reusable ordered set of parameter values applied as a template.

A canonical unit of measure, referenced from quantity values and constrained by ParameterSpec. Belongs to neither.

The assignment of one parameter key to one object class, with the local rules governing it. Aggregate root. Called assignment, never binding — binding is reserved for Revit placement.

How an assignment came to exist — direct, rendered, or legacy_unknown. Only direct rows accept deletion and allowed-value edits. Server-owned; hidden from stewards.

On direct rows only — unique (this node only) or apply_to_descendants. The retired wire vocabulary self_only / self_plus_descendants / descendants_only is gone from the HTTP contract.

On rendered rows only — inherit (default), suppress (this class only), or override (this class only, local values).

The resolved answer to "what parameters does this class actually have", computed on request with an explanation. Resolution kinds are direct, inherited, override, suppressed. Rendered rows are a cache for Airtable's benefit; the resolution is authoritative.

The Revit-facing expression of exactly one parameter key — one definition identity plus optional placements. Aggregate root; lifecycle draft → approved → archived. System-created, steward-completed.

shared, family_local, project_local, built_in, legacy_unknown. Definition means an identity BuildPlan authors and owns; Reference means an external identity it reads but never authors.

Minted once for a shared definition and never regenerated. That immutability is what makes shared definitions portable, and why retirement archives a projection rather than deleting it.

The set of Revit categories a project binding covers, resolved from effective class assignments. Derived only — the steward override was removed. Scope in this module means this and nothing else.

instance or type — Revit's own vocabulary and the one sanctioned bare use of the word "type". RevitBindingKindPreference holds the aggregate-level default.

Which Revit document kinds a projection is enabled for — family and/or project — derived at write time from the two placements, plus an authored primary preference. Same word as ParameterUsage, different altitude.

Normally derived from the canonical name, optionally pinned by override. Because it is derived, editing the canonical name drifts the projection — which is what the derivation-drift report and resync exist to reconcile.

A stewarded allowlist of platform-wide parameters in the bp.common.* handle space that project with a fixed shape. Sheet, view, and annotation categories are denylisted from common project binding.

The Airtable steward-UI mutation patterns. AT-A1 is a flag-based action table, AT-A2 a record-detail action button, AT-B1 a create-request table, AT-C1 a watched-field recompute (ADR-0047). Every one calls the API; none writes domain state directly.