This paper introduces multitrees, a new type of structure for representing information. Multitrees are a class of directed acyclic graphs (DAGs) with the unusual property that they have large easily identifiable substructures that are trees. These subtrees have a natural semantic interpretation providing alternate hierarchical contexts for information, as well as providing a natural model for hierarchical reuse. The numerous trees found within multitrees also afford familiar, tree-based graphical interactions.
George W. Furnas, Jeff Zacks