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RE: Initial draft of Design:Aggregate

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Fri, 21 Aug 2009 09:11:17 +0000
To: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3693C4C4DDA@GVW1118EXC.americas.hpqcorp.net>
I've added the definitions text to the wiki page.

	Andy

> -----Original Message-----
> From: Chimezie Ogbuji [mailto:ogbujic@ccf.org]
> Sent: 11 August 2009 14:41
> To: Seaborne, Andy; SPARQL Working Group
> Subject: Re: Initial draft of Design:Aggregate
> 
> Hey Andy
> 
> 
> On 8/10/09 9:10 AM, "Seaborne, Andy" <andy.seaborne@hp.com> wrote:
> >> http://www.w3.org/2009/sparql/wiki/Design:Aggregate

> > Hi Chime,
> > Yes - including LaTeX is hard. I think you can cut-and-paste the symbols
> into
> > the wiki text because it's all UTF-8 HTML but that's a bit fragile and only
> > marginally better.
> 
> Okay, thanks.  I'll give that a try
> 
> > I took tried to write out some formal definitions to check my
> understanding:
> > is this the sort of thing you had in mind?
> >
> >
> > Single valued function: returns a solution projected down to named
> variables
> > only:
> >   key(varlist, mu) = { (v,x) | (v,x) in mu, v in varlist }
> >
> > and the set of all keys:
> >   key(varlist, Omega) = { k | mu in Omeag, k=key(varlist,mu) }
> >
> > The partition of the multiset Omega is:
> >   Partition(varlist, Omega) = { (k,mu) | mu in Omega, k=key(varlist, mu) }
> 
> Yes, this needs to return a set from the multiset and varlist in order to
> ensure uniqueness of the partitions.
> 
> > Let agg(VarList,SubOmega) be the aggregation function run on a multiset of
> > solutions taking variables VarList
> >
> > Aggregation(VarList, FuncAndVars, Omega, Mu) =
> >    { merge(k, (Vout, agg(Vin,X)) | (k, X) in Partition(varlist, Omega),
> > FuncAndVars=(f, Vin, Vout), agg in set f }
> 
> I believe we are on the same page.
> 
> > Aside: we may need to restrict variable Vout so it does not clash with the
> > key.
> 
> Yes.
> 
> > One last point: do we want GROUP BY expressions, not just variables?  In
> think
> > we do; does create some issues about the projected down variables that are
> > arguments to the partitioning expression.
> > Some SQL systems put a random
> > selection (AKAK first found?) but I prefer to not include the variables of
> an
> > expression at all so as to get ehy same results each time.
> >
> > Andy
> 
> Good question, I don't know off head (will need to chew on that).
> 
> -- Chimezie
> 
> 
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Received on Friday, 21 August 2009 09:12:55 GMT

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