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RE: Difference between data and metadata

From: Rogers, Tony <Tony.Rogers@ca.com>
Date: Tue, 26 Sep 2006 10:10:49 +1000
Message-ID: <BEE2BD647C052D4FA59B42F5E2D946B317B64C@AUSYMS12.ca.com>
To: <paul.downey@bt.com>, <jmarsh@microsoft.com>, <christian.au@gmail.com>, <www-ws-desc@w3.org>
I was with you most of the way, but not all the way to the end. :-)
I consider metadata as the descriptive information about the data, rather than just the stuff that isn't data.
If we consider a packet travelling over the Net, carrying the data, we don't consider the start and end markers as data, but we don't consider them metadata, either. You can argue that the address fields in the packet are metadata (they "describe" the destination), but mostly they would be left out of consideration, too. The metadata here is more like the standard describing the IP part of TCP/IP.
Along those lines, I'd consider the element names to be metadata when they appear in the XSD (for XML schema), but not when they appear on the wire (on the wire they are data for the XML processor, allowing it to separate the pieces of the XML data).
Hmm - not my most articulate description, but maybe I've explained how I see it?
I definitely (and precisely) agree that /precise/ agreement isn't easy here :-)
Tony Rogers
CA, Inc
Senior Architect, Development
co-chair UDDI TC at OASIS
co-chair WS-Desc WG at W3C


From: www-ws-desc-request@w3.org on behalf of paul.downey@bt.com
Sent: Mon 25-Sep-06 21:05
To: jmarsh@microsoft.com; christian.au@gmail.com; www-ws-desc@w3.org
Subject: RE: Difference between data and metadata

I'd agree and warn it's something which we are all unlikely to
/precisely/ agree upon.

WSDL seems like classic meta-data in that the receiver
is oblivious of how the sender came to know how to
produce correctly formatted messages - the knowledge may have
been obtained using any one of a number of different
out-of-band methods, including consuming a WSDL document.

However, HTTP Content-type might also be considered by some to be
meta-data, as might XML element names and other descriptions
which appear 'on the wire' and directly influence processing.


-----Original Message-----
From: www-ws-desc-request@w3.org on behalf of Jonathan Marsh
Sent: Fri 9/22/2006 10:11 PM
To: Christian Au; www-ws-desc@w3.org
Subject: 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,
Received on Tuesday, 26 September 2006 00:10:55 UTC

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