Radio Free Meredith

Suppose you're designing a protocol, and you're deliberating over whether to use XML, YAML, JSON, s-expressions (!) or some other data representation format for it.

The question you need to ask yourself is, "have I written an EBNF definition for my protocol yet?"

If the answer is "no," drop everything you are doing. Yes, everything. Step away from the keyboard. Get a pencil and paper, or go to the whiteboard, and work out your EBNF first.

Then, and only then, you may decide what to use as a data representation. Deciding what data format to use before you have determined the grammar of your protocol is like deciding what language to use before you have figured out what algorithms you're using.

Protocol structure is a design decision. Data representation format is an implementation decision. Do not intermingle the two; it will only end in tears, yours or someone else's. Probably yours.