Heuristic algorithms result in either an independent DS or a connected DS. A subset P of V is said to be an independent set if no two vertices in P are adjacent. A connected DS is a DS in which each node is connected to at least one other node that is in the DS. (Note that if a graph consists of several connected components, a DS of such a graph would be connected within each component, but disconnected across components.) In the context of biological networks, we are interested in connected DSs.