They don’t really need each other. You can very well use arc42 with and without UML.

Graphical modelling with UML does by no means make you a better architect, nor does it (automatically) improve your systems.

You might use UML to describe or specify the following aspects of your architecture:

  • static structure (building block view)
  • runtime behavior or runtime scenarios (runtime view)
  • deployment or infrastructure
  • static or dynamic aspects of crosscutting concepts can sometimes be expressed in UML models.

See also question B-3 (UML).

Some personal comments (from Gernot)

  1. Unless absolutely required, challenge the use of (pure) UML
  2. If you use UML, be pragmatic about it (unless you generate code from models)
  3. Make “developer acceptance” an important criteria when deciding about documentation approaches.