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Burak Emir <Burak.Emir@e...> writes: > > Elliotte Harold wrote: > > > Hunsberger, Peter wrote: > > > > > >> I don't get the distinction. As soon as you've got a graph you've > >> got a tree (or perhaps many trees). > >> > > > > Not necessarily. All trees are graphs but not all graphs are trees. > > For instance a pure tree can't represent a cycle but a graph can. > > XML's rule that a node can only have one parent is not a limit of > > graphs in general. > > > I think he meant a spanning tree, i.e. one that has all the nodes but > all edges. A graph can have many spanning trees. > > This works for undirected edges. For directed, there might not be a > spanning tree in the mathematical sense, but you can still > get one if you reverse the arrows, like in this one > > o -> o <- o Nothing that sophisticated, I just meant that any tree can be contained in a graph. Guess I should have wrote something more like "As soon as you've got a tree there is a graph that can contain it (and perhaps many other trees)". Which still leaves the original question; once you've got a way of managing and manipulate graphs, why would you need a way to distinguish trees? What does recognizing the special case get you?
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