Modularity by purchase. Information hiding by ownership. Interfaces by corporation. Brooks' software system products (9x the work) is usually done this way in

Modularity by purchase. Information hiding by ownership. Interfaces by corporation. Brooks' software system products (9x the work) is usually done this way in practice. In most usage cases, I would also include open source projects. It's so hard to get interfaces right and it's helpful to have many users. But I considered your point, of it helping to enforce boundaries.