Hello Im trying to change Blobs to become an editor for a language which is not exactly a directed graph. In such system I have the notion of ports in nodes; which node have a previously fixed number of labelled ports and instead of having edges between nodes, its only allowed having edges connecting ports. For the picture of Malcolm Wallace "Failure Propagation and Transformation Calculus" in Blobs web page it seems to me that such framework addresses the same situation. So what I would like to know is if someone have ever found this problem and if someone have some idea for a way of implementing this generalization of directed graphs. One solution is create so many new nodes as the sum in the range of primitive nodes of the sum of ports for that specific node. Them it is necessary to force some constrains in the graph like the user cannot create edges from/to primitive nodes and the selection of a primitive node implies the automatic selection of it self and its port nodes. Does anyone have a better idea? Regards Miguel Vilaça