[ALL] RDF Data Access, XQuery, rules

 
Hi all, 
 
Regarding the DAWG RDF Query language, I have finally given it a good
look and below represents my own comment for ourselves to consider.
 
The draft does not give much to the reader to think about in terms of
design objectives, most of the item refers to Minutes of WG discussion
which I have no interest in diving into. It feels like the steam ran out
approaching the last third of the document.
 
I am no expert at designing query languages, but I have failed to
identify a philosophical framework of the language, it is more like a
collection of disjoint features than a well justified language. 
 
I am in two minds about whether any of the above is relevant to our
group discussion with respect to "best practices". On one hand I don't
think we should influence their internals in how to design a query
language. On the other hand, query languages will no doubt be an
important topic in any SW deployment and it would put that into our
area. 
 
However, they have asked us of our opinions on two items, so I shall
concentrate my comments to the two items they've asked for. In addition,
I will throw in one more item I have identified that we may or may not
want to take a stance on.
 
1 XQuery as one of the candidates for a "Human friendly Syntax". 
 
  As far as I am aware, they are developing an abstract syntax, on top
of which there could be several concrete syntaxes [1]. The primary
reason for considering XQuery is they have a requirement to make RDF
data accessible through XML query. And secondly due to its connection to
W3C. The technical reasons for going forward (or not) with XQuery is
complicated. Relating to the compatibility of the underlying data model,
which is out of our scope I believe.
 
  In Dan Connolly's note he wrote: "we don't have a critical mass around
any particular objective yet". This design objective is currently
"pending".
It seems like they might need some help to tip the balance either way.
Rather than technical assistance, I am inclined to offer them our view
(if any) of using XQuery to query RDF instance data from deployment
point of view (not querying any OWL ontologies). The questions for us
then becomes:
 
a)    Do any of us have any XQuery experience?
b)    (Conjecture) Xquery seems to have more industrial
adoption/traction, true or false? Is this a reason for them to consider?
Any of us have any views?
  
  If either the above answers is no, or we don't know, then we shall not
offer any views on this item.
 
 
2 It should be possible for knowledge encoded in other semantic
languages-for example: RDFS, OWL, and SWRL-to affect the results of
queries executed against RDF graphs. [2]
 
  This item currently has no status on their draft. Assume pending. 
 
  I think this item is an self evidently a "Yes it is a good objective
and you should abide by it".
 
  My reasoning is as follows: Given an ontology with instance data and a
particular query, different systems with different inferencing
capabilities may return different results.
 
  For example, a rule grandparent(x, z) if parent(x, z) and parent (z,
y)
with instance data parent(John, Mary), parent(Mary, Joe).
 
  if you ask a system without inferencing capability the question
     grandparent(x, ?) then it shall return nothing. 
  Otherwise, Joe is returned.
 
  Another example from OWL point of view, if there are two classes Tyre
and Tire, and they are equivalent, an OWL capable system should return
all instances of both Tyre and Tire if you ask for just one of them. On
the other hand, a system incapable of drawing inference on equivalences
will not be able to do that.
 
  From a development and deployment point of view I think it makes a lot
of sense to be able to use a single query language across different
inferencing system to access instance data. The choice is then to match
inferencing capability to the expressive that the problem demands.
 
3. I also noticed that they would like to address "data source
identification" within the query language. To an extent you can specify
in your query "where" you would like your data to be retrieved from
(data repository location). 
 
  Frankly, I think that would be a mistake, queries with location
information will render application development and deployment
non-portable.
 
 
Again, I am no expert in these matters, I hope I have laid out the
questions for ourselves clear enough so we can decide on a respond or
not either way.
 
Cheers
 
Gary
 
 
[1] http://www.w3.org/2003/12/swa/dawg-charter#concreteSyntax
[2] http://www.w3.org/2003/12/swa/dawg-charter#rdfs-owl-queries
 
 
 
-----Original Message-----
From: public-swbp-wg-request@w3.org
[mailto:public-swbp-wg-request@w3.org] On Behalf Of Dan Connolly
Sent: 16 August 2004 08:20
To: public-swbp-wg@w3.org
Cc: public-rdf-dawg-comments@w3.org
Subject: RDF Data Access, XQuery, rules
 
 
Hi Best Practices/Deployment folks,
 
You might  have seen our recent WD...
 
RDF Data Access Use Cases and Requirements
W3C Working Draft 2 August 2004
 
This Version: 
        http://www.w3.org/TR/2004/WD-rdf-dawg-uc-20040802/
Latest Version: 
        http://www.w3.org/TR/rdf-dawg-uc/
 
This is our 2nd release; in the Status section, note
 
"the design objectives are in development. The status of each design
objective indicates whether it has been adopted by the WG. The
requirements have all been accepted by the working group."
 
While the BPDWG is more than welcome to review the whole document,
either individually or as a group, we're particularly interested
in feedback on a couple things:
 
1. XQuery, syntax and integration: We're chartered to "... maximize
W3C technology re-use, while also taking account of differences
between the RDF graph data model and the XQuery data model" and
to allow "... for RDF data to be accessable within an XML
Query context".
 -- http://www.w3.org/2003/12/swa/dawg-charter#XQueryBinding
 
We have been discussing an objective regarding making
RDF data available in an XML Query context,
  http://www.w3.org/2001/sw/DataAccess/ftf2#qrdesigns
  http://www.w3.org/2001/sw/DataAccess/ftf2#xqfa
but we don't have a critical mass around any particular objective yet.
 
We have a "human-friendly syntax" objective
  http://www.w3.org/TR/rdf-dawg-uc/#d4.1
and there has been discussion of whether borrowing from XQuery
syntax helps there.
 
Anybody have experience with XQuery/RDF integration to share?
 
 
2. Rules, Additional Semantic Information
 
We have an objective
 
"It should be possible for knowledge encoded in other semantic
languages-for example: RDFS, OWL, and SWRL-to affect the results of
queries executed against RDF graphs."
 
 -- http://www.w3.org/TR/rdf-dawg-uc/#d4.6
 
and in discussion of rules and query
  http://www.w3.org/2001/sw/DataAccess/ftf2#qrdesigns
 
we noted a connection between rules and a CONSTRUCT
mechanism found in various contemporary designs, including
our current draft
 
http://www.w3.org/2001/sw/DataAccess/rq23/#construct
$Revision: 1.25 $ of $Date: 2004/08/16 12:23:00 $
 
Any rules/query integration experience to share? Thoughts
on best practices for accessing RDF data, while rules
work is still in the early stages of standardization?
 
 
 
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/