QGraphicsView, QGraphicsItem, QGraphicsScene

[wysota]

I always tell to my students that the scene is the world, the view is the window they're looking through at the world and the items are things that are part of the world that one sees through the window. The world is self-sufficient (you don't need to have any windows for the world to be there and be useful) and objects in the world form hierarchies where children are positioned in a "local world" of their parent -- like people on Earth, Earth in the Solar System, Solar System in the Milky Way, Milky Way in the local cluster of galaxies, etc. And people don't care that Milky Way rotates around the centre of the local cluster, they use local coordinates relative to the Earth exactly the same way as items in the scene don't care about surroundings of its parent and use local coordinates relative to their parent.