The UML in Geant4 manuals

There are many class categories in G4 manuals which introduces the class organization. However the presented UML graph is little bit different to what I know about UML syntax in other books or forums. Are there any material that explain how the UML in G4 manuals used? Thanks in advance.

Example of the class category in the manuals: Book For Application Developers(Fig 3.1), Geant4 User’s Guide for Toolkit Developers (Fig 2.5 2.6 2.7 …).