Exactly, we think in terms of interfaces. The apollo moon mission technical history is a good example. At a high level there is a big diagram with things like

Exactly, we think in terms of interfaces. The apollo moon mission technical history is a good example. At a high level there is a big diagram with things like transmissions and modules drawn as single blocks. We define how those blocks need to interact with eachother. Then teams of engineers work on each block, designing and making each block to do what it was defined to do on that big flow chart. Each part is tested to its interfaces (which can be mechanical, electrical, hydraulic, control, etc) and if each part does what it's supposed to the whole thing should.