“…Directed hypergraphs (Ausiello et al, 1985;Gallo et al, 1993) are a generalization of directed graphs (digraphs) and they can model binary relations among subsets of a given set. Such relationships appear in different areas of Computer Science such as database systems (Ausiello et al, 1985), expert systems (Ramaswamy et al, 1997), parallel programming (Nguyen et al, 1998), scheduling (Lin & Sarrafzadeh, 1995;Gallo & Scutellà, 2002), routing in dynamic networks (Pretolani, 2000) and, more recently, data mining (Chawla et al, 2004) and bioinformatics (Krishnamurthy et al, 2003).…”