public bool IsRelinkValid( NodeType newfromdata, NodeType newtodata, NodeType oldfromdata, NodeType oldtodata )
Parameters
- newfromdata
 - a node key identifying the node data from which the link would come
 - newtodata
 - a node key identify the node data to which the link would go
 - oldfromdata
 - a node key identifying the node data from which the existing link comes
 - oldtodata
 - a node key identify the node data to which the existing link goes