> A system is compositional if you can build it from small reusable parts. Take big monolith. Refactor into 1001 pieces. Glue together again. If glue is infle

> A system is compositional if you can build it from small reusable parts. Take big monolith. Refactor into 1001 pieces. Glue together again. If glue is inflexible, then result is monolith+glue. If glue is thick, then result is mostly glue + little bits of monolith. If glue is superb (well designed & flexible), the whole works the same as monolith, but pieces can easily be rearranged as needed (and individually tested!). Designing good glue is HARD! And then some.