GTypes are organized into hierarchy. Each GType (except fundamental types) has a parent type and zero or more children types. Parent of GType identified by g-type-parent function and its children are identified by g-type-children function.
There are functions to query some specific information:
g-type-fundamental retrieves the fundamental type for given type
g-type-depth calculates the depth of the type in type hierarchy
g-type-next-base calculates the first step in the path from base type to descendent type