Re: Self-descriptive messages

I lost a long argument with Mark Baker a year and a half ago on this very subject and scenario.

I argued that including the URL to a saved offer-to-buy in a message to convert it into an order was adequately self-descriptive.

At the end of the discussion, I accepted Mark's position, and abandoned my own.  

However, I thought of another reason that convinced me even more of the correctness of Mark's argument from a business standpoint, and that is non-repudiation: http://en.wikipedia.org/wiki/Non-repudiation

That is, if both parties to an electronic agreement send, receive and sign each of the full messages exchanged in the dialog, maybe even exchanging the whole built-up sequence each time, they have a record of the agreement that would be difficult for either party to repudiate.

This reason may not have been Roy's reason for including self-descriptive messages as a REST constraint, but it would be important in business contract situations.