A method of unifying edge data structures using a processor. The method begins with creation of a first edge data structure and unifying it with a second edge data structure. If during unification any of the contexted lazy copy links associated with the second graph data structure are activated, then second graph data structure is expanded. Expansion involves first selecting a contexted lazy copy link from among the contexted lazy copy links associated with the second graph data, selecting a selected attribute from the subtree feature structure pointed to by the selected contexted lazy copy link, making a copy of the selected attribute and storing the copy of the selected attribute in the second graph data structure as a second attribute, and adding a contexted lazy copy link from the second attribute to the selected attribute value.