A directed graph is weakly connected, if the undirected underlying graph obtained by replacing all directed edges of the graph with undirected edges is a connected graph.
A directed graph is strongly connected, if it contains a directed path from x <=> y for every pair of vertices (x, y). The strong components are the maximal strongly connected subgraphs.
A connected rooted graph, or flow graph, is one where there exists a directed path to every vertex from a distinguished root vertex.
VisualSim has the ability to model task graphs.
Web: https://en.wikipedia.org/wiki/Directed_graph