actually is there a schema of the graph?
you said "directed", hence there should some hierarchy in it too.'

I'm not sure I understand what you're asking, but the hierarchy is based on the relation between a category and its subcategories.

In more technical terms, in the directed graph of categories, edges are from a category to its subcategories.

I read there are 50K+ categories, maybe is there any list of "directions" aka "links" of how categories are connected?

Actually, there seem to be 1M+ categories (though not all of them are normal article categories). And category-subcategory links is exactly what the categorylinks dump contains, along with category-page links.

Petr Onderka

[[en:User:Svick]]