>>Exactly the problem. Had you started with them broken out, there would be no need to combine them.
>
>I haven't started this application.

I'm not sure what you're saying. Look around you. Most physical things are assembled from parts for use (at runtime). The individual parts have their own blueprints.

No engineer draws a single blueprint the embeds the blueprints of all the other devices.

For something as simple as a USB key the blueprint will look like

shell - usb interface - memory chip.

Some/most programmers would have...

shellusbinterfaceshellusbinterfaceconnectorsmemorychipshellmemorychipcomponentsmemorychipconnectors.

I can't even make the analogy because nobody designs things as programmers do. ;)