They can have parts and inner structure. A part in a container Model always has a Role. This containment relationship creates the hierarchical decomposition of Models. Any object must have at most one parent, and that parent must be a Model. Aspects provide primarily visibility control.
Every Model has a predefined set of Aspects.
Each part can be visible or hidden in an Aspect. Every part has a set of primary aspects where it can be created or deleted. The simplest way to express a relationship between two objects in GME is with a Connection. Connections can be directed or undirected. Connections can have Attributes themselves.