The source graph is represented by a combination of the site config -- sourceDirectory (like a vault in Obsidian, for example) and then an unconstrained expansion of a graph from the initial site page. The unconstrained "source graph" is pretty impractical, though, so we don't deal with it much... it's like with the idea of 6 degrees of separation. With no constraints almost everything connects to everything else. It's impractical to deal with.