Documents reference each other through frontmatter links, not by copying content — so metadata travels with the document and it stays understandable anywhere.
Documents link through metadata, not by copying — so each one travels self-describing.
Documents connect to each other through frontmatter links (Wikilinks, IDs, companion_to, owner), never by duplicating each other's content. The coupling lives in the metadata, so it's cheap to change one document without breaking the others, and — crucially for federation — the metadata travels with the document. A shared record arrives in another vault still carrying its own frontmatter: its type, its owner, its links, its sharing status. It's understandable on arrival without shipping the whole context around it. Loose coupling is the counterpart of Atomic documents: atoms stay small and whole; links (not copies) hold the web together. This is exactly the foreign-key discipline of a good data model, applied to documents — the Personal data warehouse pattern at the document layer.