SCC in Real-World Graphs

Real-world directed graphs often have a "bow-tie" structure with three parts:

$1.$ "In" component: Nodes that can reach the core but cannot be reached from it.

$2.$ Strongly connected core: One large SCC where every node reaches every other node.

$3.$ "Out" component: Nodes that can be reached from the core but cannot reach it.

Examples: Web graph (pages with mutual links), citation networks (papers citing each other), social networks (mutual followers). The core is usually the largest SCC.