- From: Alberto Reggiori <alberto@asemantics.com>
- Date: Wed, 23 Apr 2003 17:41:34 +0200
- To: "'www-rdf-rules@w3.org'" <www-rdf-rules@w3.org>
- Cc: Alberto Reggiori <alberto@asemantics.com>
I forward this message to the list because it is quite relevant to the
ongoing work about RDF Query interoperability
I invite people here to comment/discuss on it perhaps splitting up the
replies into different threads
cheers
Alberto
Begin forwarded message:
> From: Alberto Reggiori <alberto@asemantics.com>
> Date: Sun Apr 20, 2003 11:13:41 PM Europe/Rome
> To: danbri@w3.org, Andy Seaborne <Andy_Seaborne@hplb.hpl.hp.com>
> Cc: Alberto Reggiori <alberto@asemantics.com>, Libby Miller
> <libby.miller@bristol.ac.uk>, staff@asemantics.com
> Subject: optionals, provenance and transformation into RDF queries
>
>
> hi there!
>
> I have been reading through your IRC/chump [1] emailed to www-archive
> [2] - my strong feeling is that sooner or later we will need to add
> support at the SquishQL/RDQL syntax level for optional matching
> triples (or bindings). In addition, while developing some RDF apps I
> also found out the importance and usefulness to SELECT triples using
> one more dimension/component (s,p,o + c) aka kind of
> provenance/source/context/scope/quads information (whatever that is
> called or means in RDF :)
>
> I would like to discuss the possibility to come up with a common
> (JDBC/ODBC/DBI friendly :) syntax how to express such extensions in
> our SQL-ish query languages - I am also wondering about the use of
> some kind of CONSTRUCT clause ala SeRQL [3] to "transform" or format
> the actual bound vars. IMO this could also help the integration of RDF
> query languages with XML semi-structured ones [4] and developers would
> love that :)
>
> here, I will just quickly summarize some aspects related to this
> extensions (perhaps need to put them on the RDFQR Wiki page [5] later)
>
> optional matches
> ------------------------
> - as soon as you start writing real-world RDF applications you need
> those, otherwise you have to go back to API and "build the query by
> hand"; because RDF data nature is generally irregular, incomplete,
> perhaps expressed using different data granularity, deeply nested
> - DQL supports it and perhaps others (???)
> - RDF is flexible and tolerant and an RDF query language must be so too
> - implementation problems?
> - possible syntax
>
> ---> Andy's idea about "locating data" and "extracting data" - is it
> about splitting up the RDQL/SquishQL statement SELECT and WHERE parts
> in two?
> ---> use some special char on SELECTed vars to say they are "optional"
> (question mark at the end is not a good choice for JDBC/ODBC
> compatibility)
> ---> use square brackets (we are thinking about supporting this syntax
> perhaps flagging the SELECTed vars as optional too)
> WHERE
> (?x,<some:mandatoryProp>,?y),
> [ (?x, <some:optionalProp>, ?z)]
>
> ---> use full-blown SQL style syntax (really too verbose to me)
> WHERE
> ( (?x,<some:mandatoryProp>,?y) ) OR
> ( (?x,<some:mandatoryProp>,?y),
> (?x, <some:optionalProp>, ?z) )
>
> provenance information
> --------------------------------
> - RDF sources once parsed and stored into an RDF database are flatten
> down and at the query time you very often need to filter them based on
> the "context" where they have been asserted - i.e. source URL or some
> other RDF resource which could be further described. This information
> can not be generally represented with triples, perhaps with
> reification, but I do not understand it much :-)
> - N3 formulae are something similar
> - Quads [6] use that extra component for that IMU
> - possible syntax
>
> ---> Allow one more component on the triple-pattern ala Quads (we
> already support such a syntax in our implementation of RDQL)
>
> WHERE
> (?x, <some:prop>,?y, ?context),
> (?context, <rdf:type>,
> <some:MeaningfulContext>)
>
> ---> Allow N3 style curly brackets (ugly) - or is there any better
> syntax?
>
> WHERE ( { (?x, <some:prop>,?y, ?context) } <rdf:type>,
> <some:MeaningfulContext> )
>
> ---> Use some other special CONTEXT clause
>
> results constructors
> --------------------------
> - most applications need to use RDF just to "grep" the Web to some
> kind of XML-ish syntax - RDBMS DBI/JDBC/ODBC are also fine. But having
> an XML result allows to play a lot more with it (e.g. XSLT) and
> pipe/chain things better; and developers would feel more familiar.
> - Andy RDF Query result set could also benefit from this
> - soon people will start to nest SquisQL/RDQL statements i.e. RDF --->
> RDF transformation
> - XQuery supports it already
> - SeRQL uses it
> - possible syntax
>
> ---> ala XQuery using CONSTRUCT or TRANFORM clause
>
> SELECT
> ?x,?y
> WHERE
> (?res, <some:px>, ?x),
> (?res, <some:py>, ?y)
> CONSTRUCT
> <rs:ResultSet>
> <rs:resultVariable>x</rs:resultVariable>
> <rs:resultVariable>y</rs:resultVariable>
> <rs:size
> rdf:datatype='http://www.w3.org/2000/10/XMLSchema#integer'>1</rs:size>
> <rs:solution>
> <rs:ResultSolution>
> <rs:binding rdf:parseType='Resource'>
> <rs:variable>x</rs:variable>
> <rs:value
> rdf:datatype='{$x/rdf:datatype}'>$x</rs:value>
> </rs:binding>
> <rs:binding rdf:parseType='Resource'>
> <rs:variable>y</rs:variable>
> <rs:value rdf:resource='$y'/>
> </rs:binding>
> </rs:ResultSolution>
> </rs:solution>
> <rs:ResultSet>
> USING
> some FOR <http://somevoc.org/mine/>,
> rs FOR <http://jena.hpl.hp.com/2003/03/result-set#>
>
> ---> ala SeRQL (see spec)
> ---> any better syntax?
>
> IMO this TRANSFORM thingie would be extremely useful, especially to
> dynamically generate XML Web content out of an RDF database - it would
> also open the doors to all the others XML tools already deployed.
>
> Just give some thoughts to all this - in the meantime I will set up
> some use cases for this onto the RDF Query and Rules survey page [7]
> to see if some developer will pick it up
>
> cheers
>
> Alberto
>
> [1]
> http://rdfig.xmlhack.com/2003/04/20/2003-04-20.html#1050846336.312674
> [2] http://lists.w3.org/Archives/Public/www-archive/2003Apr/0052.html
> [3] http://lists.w3.org/Archives/Public/www-rdf-rules/2003Apr/0013.html
> [4] http://www.w3.org/TR/xquery/
> [5] http://esw.w3.org/topic/RDFQueryTestcasesRequirements
> [6] http://robustai.net/sailor/grammar/Quads.html
> [7]
> http://rdfstore.sourceforge.net/2002/06/24/rdf-query/query-use-
> cases.html
Received on Wednesday, 23 April 2003 11:41:42 UTC