Mappings provide two means of model traversal. The accept(ResourceMappingContext, IResourceVisitor, IProgressMonitor) method
can be used to visit the resources that constitute the model object. Alternatively,
a set or traversals can be obtained by calling getTraversals(ResourceMappingContext, IProgressMonitor) . A traversal
contains a set of resources and a depth. This allows clients (such a repository providers)
to do optimal traversals of the resources w.r.t. the operation that is being performed
on the model object.
This class may be subclassed by clients.