ADR 0034: Authored open profiles are graph declarations, not areas

• Status: Accepted
• Date: 2026-09-01
• Deciders: Axiolid maintainers
• Supersedes: —

Context

A source model can declare an exact bounded open two-dimensional path as a profile. Such a declaration carries neither an enclosed area nor a width. Closing it would fabricate an edge and an area; treating it as a centre line would fabricate width semantics.

Axiolid already has two relevant but intentionally different vocabularies:

• axiolid-profile::Profile describes sweep sections with area semantics;
• axiolid-model can preserve atomic and relational exact 2D curves, including trimmed, composite, offset, and parameter curves.

Putting a graph NodeId in axiolid-profile would reverse crate layering. Copying a relational curve into an owned atomic profile value would lose exact composition and trim intent. Reusing mesh-plane section contours would replace authored exact geometry with evaluated approximate linework and would cross the IFC/plan boundary forbidden by ADR 0033.

Decision

We will represent an authored bounded open profile as axiolid_model::OpenProfile, a graph payload whose path references a prior exact 2D curve-family node.

• GeometryNode::OpenProfile is distinct from GeometryNode::Profile.
• It carries no area, width, closure edge, tessellation, or manufacturing semantics.
• Graph construction accepts only conservatively bounded-open 2D paths:
  • source-open polylines with at least two finite controls and distinct authored endpoints;
  • source-open B-splines with finite controls and knots, coherent degree/knot/multiplicity cardinalities, and optional strictly positive finite weights;
  • trimmed 2D curves whose start and end selectors are finite, 2D-compatible, present in the declared preferred representation, and not exactly equal in a shared representation;
  • non-empty composites, finite-distance 2D offsets without a 3D reference direction, and parameter curves whose referenced paths satisfy the same contract;
  • instances preserve the referenced curve family and require finite transforms.
• Curve-family and bounded-open validation visit each reachable graph node at most once per check, so shared append-only DAGs do not expand into exponential work.
• Infinite lines, atomic circles/ellipses, source-closed or exactly self-closing polylines, source-closed or structurally invalid B-splines, non-finite curve/offset/instance data, 3D offset reference directions, empty composites, missing or non-finite trim endpoints, 3D trim selectors, exactly equal parameter/point trim endpoints, 3D curves, and non-curves are rejected.
• Endpoint coincidence and relational closure that cannot be established from identical authored selectors remain evaluator validation responsibilities. The payload preserves the source declaration; it does not claim a numerical proof that arbitrary relational endpoints differ.
• Existing solid operations continue to accept only area Profile nodes. Passing an OpenProfile to extrusion, revolution, or any other area-profile edge is a graph type error.
• The scalar mesh compiler reports standalone open-profile compilation as missing CurveEvaluation; it never triangulates or closes the path.

Alternatives considered

Option	Why not
Add an open variant to axiolid_profile::Profile	Makes area-only generator inputs admit a no-area state and pushes runtime rejection into every consumer.
Store Curve2 directly in axiolid-profile	Cannot preserve graph-level trimmed/composite/offset curve relations without copying or flattening.
Store NodeId in axiolid-profile	Reverses the L1 representation → L2 graph dependency direction.
Reuse CenterLineProfile	A centre line implies a width and area; an authored open profile does not.
Close the path	Fabricates an unstated edge and enclosed area.
Use mesh-plane section contours	Substitutes evaluated approximate linework for authored exact geometry and confuses representation with plan derivation.

Consequences

Positive

• Importers can preserve exact open-profile intent without format-specific types.
• Invalid use as an area profile is rejected at graph construction.
• Existing area-profile and generation APIs remain semver-compatible.
• Composite and trimmed source curves remain graph references rather than flattened approximations.

Negative / costs

• Consumers that need points must explicitly request curve evaluation.
• Exact endpoint openness for arbitrary relational curves cannot be proven structurally and requires an evaluator.
• Importers must lower the path curve first and then append the declaration node.

Follow-ups / risks to watch

• Add a result-bearing bounded evaluator if consumers need a certified open-path endpoint/closure report.
• Do not broaden solid-operation profile edges to accept OpenProfile.
• Do not infer plans, regions, offsets, or manufacturing layers from this declaration.

Relation to existing code

• crates/representations/modeling/graph/src/node.rs owns OpenProfile and GeometryNode::OpenProfile.
• crates/representations/modeling/graph/src/validation.rs enforces graph-reference and conservative bounded/open semantics.
• crates/representations/modeling/graph/src/value.rs provides sealed builder insertion.
• crates/execution/compile/src/compiler.rs classifies evaluation without manufacturing a mesh.
• ADR 0009 defines the graph layering; ADR 0033 separates authored geometry from mesh-derived section contours.