1. A method of implementing node related conditions in a directory server having a tree structure using condition-defining data attached to nodes, the method comprising: attaching condition-defining data to a given node in the tree structure, said condition defining data having a variable portion and a reference portion; upon access to a subnode of said given node in the tree: tentatively deriving a value for the variable portion, using the reference portion and a property of the subnode, changing the variable portion into the value; and evaluating the condition in said condition defining data as interpreted.