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RE: Grammar support for querying property values that are XML str uctu res?

From: Stephan, Eric G <Eric.Stephan@pnl.gov>
Date: Thu, 15 Jun 2000 23:39:25 -0700
To: "'Babich, Alan '" <ABabich@filenet.com>, "'www-webdav-dasl@w3.org '" <www-webdav-dasl@w3.org>
Message-id: <9E9DBE33F0E9D211AC5F0008C7A4E1F4653BE3@PNLMSE10.pnl.gov>
 Thank you for sharing your perspective with me.  My earlier message was not
meant to distract or hender the wheels of progress on release 1.0 of the
protocol, but merely to understand the implications of the queries discussed in
the protocol specification as it pertained to XML based values. We will simply
need to look for other solutions to supplement our particular needs for the time
being.

With this said, what specific activites are left to do on the DASL protcol to
move it from 0.0 to 1.0?  I am motivated by the fact that without something like
DASL, DAV will be a limited web capability.  If I can be of any assistance let
me know.

Regards,

Eric Stephan


-----Original Message-----
From: Babich, Alan
To: Stephan, Eric G; www-webdav-dasl@w3.org
Sent: 6/15/00 12:28 PM
Subject: RE: Grammar support for querying property values that are XML str uctu
res?

It is necessary to put this issue in context. Due to the 
swift pace of things today, especially related to the 
internet, one can not have the ultimate final product 
on release one, whether it be a spec. or a real product. 
It is only realistic to shoot for the essentials on the 
first release. If you are too ambitious, the market will 
do something else, and you will miss your product window 
entirely (For a spectacular failure of this type, recall
the billions that were lost on the Motorola Iridium
satellite network. It took too long, and so was
obsolete by the time it was deployed, and had to be 
killed.)

So, DASL and other WebDAV efforts have the rule "For
the first release, cut features until it wouldn't be 
useful".

This is not all bad. That way you can get real feedback
ASAP on what the most important things are that need 
to be added from actual experience.

That is the first reason DASL deliberately did not
tackle hierarchical property values. (BTW: Hierarchical
property values don't have to be stored in XML.
Some DBMS's stored hierarchical properties
decades before XML was even invented. So the WebDAV 
property model makes the distinction.)

The second reason is that there was an XML query
language effort in progress at the time. True, a query
language is not a protocol, and a protocol is not
a query language, so there is no conflict.
Nevertheless, some people perceived a conflict.
Furthermore, the DASL protocol might benefit from
cross pollination from an accepted XML query language,
so it might be beneficial to wait for resolution
of that effort.

A couple of proposals were floated about how to add
query of hierarchical properties to DASL's basic
search. They are proof that there is more than one
way to add that feature to basic search -- a separate
grammar is not needed. After discussion, it was 
decided that the right thing to do was to defer it 
to the second release.

Remember, only the most basic of searches is specified 
in the DASL draft. Every DASL implementation will have to
implement basic search and the rest of the non optional
features in the first draft. Optional features
are generally undesirable, and were minimized. DASL has
escape mechanisms, so that any number of 
different query protocols can be added later. Furthermore, 
provision has been made for adding optional features 
to basic search. If DASL is accepted, then it is 
predictable that it will be extended on later releases.

Alan Babich

-----Original Message-----
From: Stephan, Eric G [mailto:Eric.Stephan@pnl.gov]
Sent: Thursday, June 15, 2000 10:41 AM
To: www-webdav-dasl@w3.org
Subject: Grammer support for querying property values that are XML
structu res?


My basic question is:  Will (does) the DASL protocol define a grammer be
used to
query and return parts of a property value if that value is an XML
structure?  

It seems to me that the DASL basic grammer is geared to query simple
unstructured property values (e.g. strings, numbers, possibly dates),
but
not
structured values such as an XML structure.  To support this (if my
impressions
are correctabout the basic grammer) a separate grammer needs to be
created
to
allow me to do this.

Please let me know if I have overlooked something and my impressions are
incorrect.  If I am correct I'd like to hear from you on how to deal
with
XML
structured values in queries, grammers that are being explored, leaving
the
problem to the client etc.

Below I have included an example of the problems we hope DASL can solve
for
us.

Thanks,

Eric Stephan
Sr. Research Scientist
Battelle - Pacific Northwest National Laboratory
P.O. Box 999, MS K1-96
Richland, WA  99352
Phone:    509-375-6977
Fax:        509-375-6631
Email:     eric.stephan@pnl.gov


Here is our problem using DAV today:

Given the non-hierarchical view of properties on a given
document/collection
we
are taking advantage of storing structured values in XML as shown below:

<DAV:prop>
  <bogus:foo-model>
    <name>calculation</name>
    <version>1.0</version>
    <foo-author>
      <name>Math Ematics</name>
      <email>mailto:mathematics@bogus.com</email>
    </foo-author>
  </bogus:foo-model>
</DAV:prop>


Some problems that a XML value query grammer could help solve:
	1) How do you query a property value stored in an XML structure
that
contains an XML element whose value is equal, not, equal, like, >, <
etc..
	Two examples come to mind:
		-Find collections/documents with the bogus:foo-model
value
whose
value contains <name> = "calculation" AND <version> not equal to 0.0.
		-Determine which bogus:foo-model <version> is greater
than
0.0

	2)  How do you return only part of the property value in the
result
of
the query?  
		Example:  Return the foo-model name and foo-model
foo-model
foo-author name

What I want the format my my query result property value to look like
when
it is
returned from DAV:
  	 <bogus:foo-model>
     		<name/>
     		<foo-author>
       			<name/>
		</foo-author>
   	</bogus:foo-model>
Received on Friday, 16 June 2000 02:40:04 GMT

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