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RE: Proposed XQuery requirement and/or objective

From: Jim Hendler <hendler@cs.umd.edu>
Date: Mon, 19 Jul 2004 19:01:57 -0400
Message-Id: <p06110414bd22020051e1@[172.26.0.20]>
To: "Jeff Pollock" <Jeff.Pollock@networkinference.com>, <public-rdf-dawg@w3.org>
Jeff-
  again, let me register my neutrality on this 
issue - I can see many ways it could possibly go 
that we could both live with given what we've 
written so far.  However, my real problem with 
taking it further is that since Kendall has 
walked into my office and drawn on my white board 
a bunch of examples (from the use cases)  I have 
a comfort level there, but I don't have examples 
of what you want to see what mappings might look 
like.  Maybe it is because I joined late, but I 
don't have such examples for the Xquery type 
syntax, so it is hard for me to really make 
informed judgements -- in light of your number 1 
below "happy medium of Xquery syntax... and 
simple semantics" I wonder if you and/or Rob 
could just draft an example or two of what this 
might look like for those of us who weren't at 
the f2f - I don't mean a strawman proposal, just 
an outline of how you might do one or two of the 
first use cases in the document, so I and the 
others who haven't seen it can get a feel -- if 
you have done this before or presented at the 
f2f, just a pointer or quick recap would be good 
to help those of us who missed it.
  I'd feel a lot more comfortable exploring the 
below with an example or two in hand
  thanks
  JH

At 9:36 -0700 7/19/04, Jeff Pollock wrote:
Jim-

No, I don't think we are too far off here. If you 
are in favor of a [surface layer/grammar/concrete 
syntax] for the DAWG proposed query language that 
builds upon a widely-adopted format, then we are 
agreed in principle.

Tactics on the other handŠ ;-)

We think XQuery is a better basis for a surface layer for several reasons:

(1)     XQuery is more modular than SQL. It lends 
itself to a richer use of its grammar and simple 
query semantics, without adopting the data model, 
than does ANSI SQL. We are _not_ proposing a 
simple "looks like XQuery" surface layer here, 
_nor_ are we proposing a wholesale adoption of 
the XQuery data model and XPath. Instead, we feel 
like a happy medium of XQuery syntax (language 
constructs) and grammar (keywords) and simple 
semantics (meanings to keywords) should be the 
basis of the DAWG surface layer.  For this point, 
I wholly defer to Rob Shearer - who is an expert 
on implementing XQuery over inference engines and 
SemWeb data structures - he will correct and 
augment my language as needed.

(2)     XQuery is a W3C spec. We believe in 
supporting the W3C initiatives and making use of 
the layered architecture principles advocated by 
this organization. Barring any technical barriers 
that are insurmountable, we think that XQuery 
should be the natural starting point for this 
surface syntax. (apparently the authors of the 
DAWG charter did as well)

(3)     XQuery is more "general purpose" than 
SQL. We believe that the Semantic Web (engines 
and language specs) will be about far more than 
databases or data access. Our customers use our 
XQuery-based inference engine for many 
non-database use cases. For instance, the use of 
OWL/RDF for encapsulating business rules than can 
be deduced at runtime by enterprise applications. 
Likewise, many of our customers are using OWL as 
a query mediation schema for heterogeneous data 
access to web services. Neither of these cases is 
database-like in its implementation. We foresee a 
future where the Semantic Web does far more than 
provide "federated databases" or "data 
integration" style applications. We think that 
business rules, business logic, web services 
interface management, process management and so 
forth are important aspects of the long-term 
development of the Semantic Web vision that 
require a more general purpose query language 
than SQL.

(4)     XQuery has a native XML context. 
Regardless of all the political infighting that 
occurred, the output of RDF and OWL (and most 
likely SWRL) specifications was solidly grounded 
upon XML inside the SemWeb layer cake. As the 
foundation of the layer cake, XML serves as a 
common syntax for all SemWeb languages, it makes 
sense to ground the query layer in a similar 
syntactic (or surface layer) basis. Further, 
since the commitment was made to XML in this 
capacity, we think it a natural fit to choose a 
unified query concrete syntax that is grounded in 
the native data representation syntax for 
semantic web specifications.

I feel like there are many other good supporting 
arguments and rationale for XQuery, so I reserve 
the right to add to this list later.  ;-)

But for now, these are some of the important 
reasons why XQuery would be a better surface 
syntax than SQL for the DAWG query output.

Regards,

-Jeff-




From: Jim Hendler [mailto:hendler@cs.umd.edu]
Sent: Thursday, July 15, 2004 3:07 PM
To: Jeff Pollock; public-rdf-dawg@w3.org
Subject: RE: Proposed XQuery requirement and/or objective

At 14:47 -0700 7/15/04, Jeff Pollock wrote:
Jim-

Points taken, and no hostility inferred.

Your counterpoints regarding the adoption of SQL are a great debate to have.

In broad brush-strokes, we are committed to a 
query concrete syntax which is grounded in a 
widely-adopted (and preferably W3C recommended) 
representation.

Further, in no means do I intend to imply that 
XQuery would make things easier on the vendor 
implementations for RDFS/OWL/Rule components of 
the SemWeb - quite the opposite, the 
implementations may even be more difficult.  Our 
point is intended to speak towards our opinion 
that a known query representation would speed 
user adoption rates for semantic web languages.

If early adopters of large commercial 
organizations were faced with learning and 
implementing a wholly new syntax for queries - on 
top of what they already have to pay for in human 
resource expertise - we suspect, and have 
encountered, resistance.

Anecdotally, we would likely be supportive of the 
OWL "two surface realizations" model, as long as 
one of them was a widely-adopted standard format.

-Jeff-

sounds like we're near the same page -- guess 
what I'm having trouble w/is the "widely-adopted 
standard format" -- since I haven't seen the 
Xquery proposal, I've been assuming it is some 
sort of specialization of Xquery much as RDQL is 
a "SQL-like" langauge -- guess I'm thinking that 
most large commercial orgs have lots of people 
who speak SQL and could learn RDQL-like langauge 
without thinking of it as different (I speak from 
experience, I've met a lot of govt folks who have 
used RDQL with RDF DBs because "they didn't need 
any training" - which is more or less a direct 
quote from someone telling me why he didn't take 
a SemWeb training course some colleagues were 
teaching) where Xquery is not yet on their todo 
list.  On the other hand, it is clear more people 
will move to Xquery as XML DBs slowly get 
accepted and steal market share from traditional 
RDBMS DBs (although right now it is pretty clear 
which one if David and which is Goliath) .. so I 
think I would agree with you that "as long as one 
of them was a widely-adopted standard format", 
although I'm less sure we would agree which is 
which :->
  -JH


--
Professor James Hendler			  http://www.cs.umd.edu/users/hendler 
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-277-3388 (Cell)



-- 
Professor James Hendler			  http://www.cs.umd.edu/users/hendler 
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-277-3388 (Cell)
Received on Monday, 19 July 2004 19:03:19 GMT

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