Complex sentence: The HOOPS 3D Application Framework has three main elements the first of which is the core HOOPS 3D Graphics System itself, a 3D scene-graph API.
Split into simpler sentences: The HOOPS 3D Graphics System is a 3D Graphics API, part of The HOOPS 3D Application Framework. The first is the core HOOPS 3D Graphics System, a 3D scene-graph API.