A widely accepted opinion is that, under a certain ordering restriction, the class of Reduced Ordered Binary Decision Diagrams (ROBDDs) is closed under composition. However, in this paper we show that this is not correct. We formulate necessary and sufficient conditions for the composition of two ROBDDs to result in a non-reduced OBDD. Ignoring these conditions may lead to an incorrect conclusi...

Modularity is a recently introduced quality measure for graph clusterings. It has immediately received considerable attention in several disciplines, and in particular in the complex systems literature, although its properties are not well understood. We study the problem of finding clusterings with maximum modularity, thus providing theoretical foundations for past and present work based on th...

The purpose of this paper 1 is to illustrate the beneets of a Petri net based approach for control and monitoring of event-driven operations in process systems. A Petri net based speciication contains structural information which is absent from a simple state transition graph. The veriication scheme is not necessarily based on a state enumeration and many results can be obtained by analysing pa...

We describe a methodology for the automatic identification of communities of practice from email logs within an organization. We use a betweenness centrality algorithm that can rapidly find communities within a graph representing information flows. We apply this algorithm to an email corpus of nearly one million messages collected over a two-month span, and show that the method is effective at ...