RE: Difference between data and metadata

Good point.  It illustrates that the data/metadata relationship holds within a context.  In the context of web service message exchanges, you could say the messages being exchanged are data and the descriptive artifacts such as WSDL and Schema are the metadata.  But within the context of a single message, there may data (like a payload) and metadata about that data (like, whether it is authentic).  Another good example is xml:lang.  It provides metadata about data within the context of an XML element - and the XML element itself can be thought of as metadata about the structure of the data it contains.

________________________________
From: Ramkumar Menon [mailto:ramkumar.menon@gmail.com]
Sent: Monday, September 25, 2006 7:31 PM
To: Rogers, Tony
Cc: paul.downey@bt.com; Jonathan Marsh; christian.au@gmail.com; www-ws-desc@w3.org
Subject: Re: Difference between data and metadata

Hi All,

My 2 cents.

1) In the context of web services, Messages that are sent between, or among endpoints could be termed as data.
2) Metadata describes the what, how and where for the data [message].Note that in this case, metadata should be interpreted as more of metadata for the interaction, than about just being [but includes] the metadata/description for the data[message]. For instance, where the message is originating from, where its heading to, how to secure the message, description of the message,how to perform message non-repudiation etc are considered metadata.
3) Wire messages could contain data, possibly along with the metadata of the data that is being sent across, as headers, as a part of the message itself, or as references that can be resolved by the consuming entity/intermediaries.

With this perspective,
a) WSDL is not really ". the data which is enhanced via metadata", as Christian refers to, but is the metadata itself, since it describes the message, describes the service that supports the message exchange etc, and describes where the message can be addressed to etc.
b) WS-Security too, with the support of point in (2) and (3) are metadata .
3) WS-CDL, BPEL etc are metadata of your business processes/collaborations that define an observable message exchange [exchange of data] among parties in a distributed environment. Hence, they too fall under metadata.  [of the interaction]

-Ram

On 9/25/06, Rogers, Tony <Tony.Rogers@ca.com<mailto:Tony.Rogers@ca.com> > wrote:
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
tony.rogers@ca.com<mailto:tony.rogers@ca.com>
co-chair UDDI TC at OASIS
co-chair WS-Desc WG at W3C

________________________________
From: www-ws-desc-request@w3.org<mailto:www-ws-desc-request@w3.org> on behalf of paul.downey@bt.com<mailto:paul.downey@bt.com>
Sent: Mon 25-Sep-06 21:05
To: jmarsh@microsoft.com<mailto:jmarsh@microsoft.com>; christian.au@gmail.com<mailto:christian.au@gmail.com>; www-ws-desc@w3.org<mailto: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.

Paul

-----Original Message-----
From: www-ws-desc-request@w3.org<mailto: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 <mailto: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> [ 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<mailto: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






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-Ramkumar Menon
A typical Macroprocessor