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.
Kingsley
Regards,
Andreas.
--
Regards,
Kingsley Idehen Weblog: http://www.openlinksw.com/blog/~kidehen
President & CEO
OpenLink Software Web: http://www.openlinksw.com
