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Re: SPARQL for faceted browsing

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Sun, 31 May 2009 20:14:34 -0400
Message-ID: <4A231D6A.2040902@openlinksw.com>
To: Andreas Harth <andreas@harth.org>
CC: Dan Brickley <danbri@danbri.org>, Daniel Schwabe <dschwabe@inf.puc-rio.br>, David Huynh <dfhuynh@alum.mit.edu>, Linked Data community <public-lod@w3.org>, semantic-web@w3.org
Andreas Harth wrote:
> Hi,
> Dan Brickley wrote:
>> Basic idea in a nutshell is that SPARQL is great for data access, but 
>> there may be additional query-oriented data structures worth spec'ing 
>> based around the set-oriented navigation very nicely articulated by 
>> David Huynh in the Parallax screencast. And that if such a structure 
>> could be exchanged between systems we could hope that the 
>> navigational paradigm it supports could be found in various concrete 
>> UIs, and that the results of exploring data this way could become 
>> useful and standard artifacts in the public Web, rather than just 
>> bookmarks within some specific system.
> there's at least two issues with using standard SPARQL endpoints
> in a faceted browsing system (as far as I can see from my experiements
> with SWSE and VisiNav):
> * A lot of end-user systems for RDF data navigation offer keyword
> search, which is not in standard SPARQL.  Emulating fulltext search
> with SPARQL regex's seems suboptimal.  Using endpoint-specific
> FILTERs or magic predicates requires adaptations depending on
> the RDF store used, and might be tricky when you want to mix
> SPARQL endpoints from different vendors.
Yes, but we have to make a choice here, wait for the standardization 
process, or get on with business?

We've chosen to get on with business. The realm of data access is sorta 
old and many of the old patterns from the RDBMS realm are still 
trickling through the SPARQL comprehension and alignment process.

So magic predicates cannot be helped at this juncture, especially if 
Linked Data is to be taken seriously outside the SemWeb community. 
Example: serious business intelligence. Note the PwC report talks about 
Linked Data and BI, meaning lots of assumptions are being made about 
Linked Data in this realm already.
> * Ranking is essential for systems offering navigation over web data.
> LIMIT is ok to improve performance by keeping the result size small,
> but query processors will then return arbitrary results that wouldn't
> satisfy end users who expect relevant (i.e. ranked) results.
Yes, hence Entity Rank in Virtuoso.  Entity Rank slots should be part of 
any abstraction above SPARQL.

As for LIMIT and OFFSET, the concept of Scrollable Cursors (Static, 
Keyset, Mixed, and Dynamic) for sliding Windows over data sets has been
long established in the RDBMS realm (although partially implemented by 
most, ditto ODBC and JDBC drivers that talk to RDBMS engines). Again, 
we've covered these
basis in Virtuoso with the broader community in mind :-)

Linked Data needs its ODBC or JDBC equivalent, this will leave interface 
implementation to Quad Store vendors and middleware players. If done 
right, it will simply solidify the reality that the RDBMS era is over 
re. primacy within the data access and integration pyramid.

> Regards,
> Andreas.



Kingsley Idehen	      Weblog: http://www.openlinksw.com/blog/~kidehen
President & CEO 
OpenLink Software     Web: http://www.openlinksw.com
Received on Monday, 1 June 2009 00:16:29 UTC

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