Web Things, by Mark Baker

A good comment from Chui Tey over in Steve’s comments.

Interfaces defining many kinds of messages imposes unncessary [sic] coupling, when what is required is for documents to be thrown over the other side of the wall, leaving the other party to decide what order to parse and process the document.

So in the spirit of the Zero/One/Infinity rule, what is he saying? Is it a) services should not have interfaces, b) services should share a common interface, or c) services should have whatever interface they want?