ER Diagram

Cardinality is the part people get wrong. Write it explicitly.

• Format.puml
• Length36 lines
• Includesnone

The source

36 lines of PlantUML, and needs nothing beyond the bundled engine. Copy it, or open the template inside Gnomon and render it as it is.

@startuml

title Entity Relationship Diagram

entity "User" as user {
  * id : INT <<PK>>
  --
  * email : VARCHAR(255)
  * password_hash : VARCHAR(255)
  created_at : TIMESTAMP
}

entity "Post" as post {
  * id : INT <<PK>>
  --
  * user_id : INT <<FK>>
  * title : VARCHAR(255)
  content : TEXT
  published : BOOLEAN
  created_at : TIMESTAMP
}

entity "Comment" as comment {
  * id : INT <<PK>>
  --
  * post_id : INT <<FK>>
  * user_id : INT <<FK>>
  content : TEXT
  created_at : TIMESTAMP
}

user ||--o{ post : writes
user ||--o{ comment : writes
post ||--o{ comment : has

@enduml

Others in UML and standard diagrams

• Sequence DiagramThe highest-value diagram in this list. Time runs down; participants across.
• Activity / Flow DiagramEarns its place when there are real branches and joins.
• Use Case DiagramActor-to-goal. Dated, but still the clearest way to show scope boundaries.
• Class DiagramBest used for a single bounded context, not a codebase.
• State DiagramForces the awkward questions about duplicate and out-of-order events.
• Mind MapFor structuring thinking, not for documenting a system.
• Gantt ChartPlans, not architecture, but it renders from text, so it diffs in review.
• JSON VisualizationVisualises a JSON payload: handy in an API design review.
• Work Breakdown StructureWork breakdown. Useful for scoping a piece of delivery.