This interface defines the functions that can be used to interact with a data
store XML resource that summarises the information expressed by an XLink
network relationship graph. The nodes of the graph are the fragments
connected by the XLink relationships.
Each node in graph summary has a name that is the index of the node fragment,
prefixed by an underscore '_'.
parent - The element in the graph resource representing the parent.
the set elements in the graph resource representing the children.
The children are ordered by the order attribute on the arcs
expressing the relationships. Where the order attribute is
identical for two relationships, the child index ordering cannot
be relied upon to be consistent.