RE: Difference between data and metadata

>From a Web Services point of view, I believe what travels on the wire is data (e.g. SOAP messages in HTTP envelopes).  What describes what goes on the wire is metadata (WSDL, WS-Policy, CDL).  In a few instances metadata might appear on the wire, but generally only to facilitate future interactions, not to make that particular exchange work.

I believe WSDL is purely metadata, through the thought experiment.  If I took the WSDL away, would the described on-the-wire exchange still be able to occur?  In almost all cases an omniscient coder could still craft the required messages and successfully exchange them.  The metadata, in its various flavors, is not strictly necessary to the successful exchange, but describes different parts of the exchange in formats that allow an ignorant coder (e.g. a toolkit) to raise it's level of awareness towards omniscience.

We all know there are limits to today's metadata formats, especially in terms of legal obligations and business purpose, that will continue to be indescribable.  This information is missing (in machine-readable form) and yet the exchange can still take place, thus it also falls under my definition of "metadata".

Hope this helps.

________________________________
From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org] On Behalf Of Christian Au
Sent: Thursday, September 21, 2006 1:48 AM
To: www-ws-desc@w3.org
Subject: Difference between data and metadata

Dear all,

I am kind of confused about the definition of metadata in the context of web services and would be very grateful for any clarification.

First question would be, if the WSDL-specification already is metadata regarding to my web service or primary a definition of my web service ( i.e. the data which is enhanced via metadata)?  WS-Policy and WSDL-S annotations clearly seem to be metadata, but what about a description of the choreography with ws-cdl or a definition of security mechanism with ws-security? data or metadata?
how would you classify standards like ws-management and ws-reliablemessaging?

In the standard I could not find any clear specification of this term...

Thanks and kind regards,
Christian