Re: Visibility (was Re: Introducing the Service Oriented Architec tural style, and it's constraints and properties.

(sorry Chris, I meant to send this to the list)

On Tue, Feb 25, 2003 at 10:48:46AM -0500, Christopher B Ferris wrote:
> Okay, let me ask once more, what is the action being performed on a HTTP 
> POST?

POST is the action.

For example, POSTing a purchase order to a purchase order processor.  The
only action in that interaction, is "POST"; the URI identifies the
processor, and the body on the POST request is a representation of a
purchase order (with no method).

> The RFC specifically 
> states that it is determined by the server and can be just about anything 
> it wants it to mean.

Yes, but if the action is anything other than POST (like "getStockQuote",
etc..), then visibility is reduced.  POST is the catch-all HTTP method,
but it does have a use separate from tunneling, and using it in that way
is how visibility is maintained.  Moreover, for every action you tunnel
through the POST body, I can show you a solution to the same problem
using HTTP (likely more than just POST), without an action in the POST
body.  That solution is more visible.

> There may be
> apparent visibility, but in truth, there is none. All that can be said of 
> the HTTP POST method is that the method 
> is not GET, PUT, DELETE, HEAD or OPTIONS. If anything, when using POST, 
> having the entity body
> well understood and easily parsable increases visibility rather than 
> reducing it. Ad hoc entity body or
> various form encoding is IMO far less visible because it is not 
> standardized.
> 
> As has been pointed out, Web services is also not exclusive to HTTP and 

Yes, of course.  That's why the "action" on an SMTP message-send is
DATA, unless another one goes in the body or subject line, like
"subscribe www-ws-arch".

> one of the objectives
> is that the service should be capable of being bound to any number of 
> underlying protocols without
> requiring that the service itself be changed.

Whoa, where'd that last part come from?  Reference please.  I agree
that protocol independance is a good thing, but not such that there's
no semantic difference between using HTTP and SMTP, for example.  Of
couse there's a difference; they're different applications.

MB
-- 
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Web architecture consulting, technical reports, evaluation & analysis