---
id: SCH-43
family: GR-SCHEMA
level: extended
profiles: [storage-api, editor-client]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-schema/sch-43
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# SCH-43 — Shape compatibility is nominal and mostly derived

*GR-SCHEMA (Part I) · level: extended · profiles: storage-api, editor-client · added in 1.0*

Two shapes match because they carry the same name, never because their schemas happen to agree; otherwise edge legality would drift every time a schema gained a field.

## The rule

> **Normative.** This is the rule.
>
> 1. A shape is compatible with another because they share an id, never because two schemas were compared.
>
> 2. Structural matching would make edge legality depend on schema evolution: two unrelated shapes that coincide today would silently interconnect, and silently disconnect when one gained a field.
>
> 3. Every shape matches itself, and derives a one-way widening into `json` and into the sink: a consumer already typed `json` must keep accepting a shaped value without being rewired, and the reverse is refused because a bare object carries no guarantee of the shape.
>
> 4. Any further widening is a hand-written rule that states its reason where it is declared.
>
> 5. Shapes join the lane list before the sink and control rules are generated, so a new lane receives those by construction rather than by a second derivation.

## Related rules

- Names: SCH-39, SCH-42
- Referenced by: SCH-39, SCH-42

---

Rule identifiers are permanent and are never renumbered. This specification carries
no implementation status: each implementation publishes its own standing against
these rules. Licensed CC BY 4.0.