references/type-er.md

ER / Data Model

Best for: conceptual and logical data models, API resource relationships, domain models — anything where the story is entities and cardinality.

Not for the physical schema. ER is entity-level: relationship lines join boxes and carry cardinality at each end. When the point is real tables with SQL types, constraint chips, indexes, and foreign keys that anchor column to column, use type-db-schema.md instead.

Layout conventions

• Each entity is a two-section box:
  • Header: type tag (ENTITY) + entity name in Geist.
  • Body: field list in Geist Mono, one per line. PK prefixed with #, FK prefixed with →.
• Relationships: lines between entities with cardinality at each end:
  • 1, N, 0..1, 1..* in Geist Mono, 8px, placed 10–12px from the entity edge.
  • Optional relationship label ("has", "belongs to") centered on the line.
• Group related entities close; lay out so most relationships are straight lines, not tangles.
• Coral on the aggregate root or central entity of the model.

Anti-patterns

• Drawing an arrow for every FK on a model with dozens — lay out by cluster instead.
• Inconsistent cardinality notation between ends of the same relationship.
• Fields padded to equal-height boxes — natural height by content is fine.

Examples

• assets/example-er.html — minimal light
• assets/example-er-dark.html — minimal dark
• assets/example-er-full.html — full editorial