Software Design Boundaries

Goal

Place code together or apart based on shared knowledge, ownership, and interface simplicity.

Boundary Questions

• What information must be hidden to keep callers simple?
• Which code changes for the same reason?
• Which data or invariant has a single rightful owner?
• Does this layer add a different abstraction, or just rename the layer below?
• Is complexity being pulled downward or leaked upward?
• Are special-purpose decisions mixed into general-purpose mechanisms?

Bring Together When