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Re: Initial draft of Design:Aggregate

From: Ivan Herman <ivan@w3.org>
Date: Tue, 25 Aug 2009 12:34:57 +0200
Message-ID: <4A93BE51.4040301@w3.org>
To: Chimezie Ogbuji <ogbujic@ccf.org>
CC: "Seaborne, Andy" <andy.seaborne@hp.com>, SPARQL Working Group <public-rdf-dawg@w3.org>
I wonder... I realize that this 'HAVING' is powerful, but may lead to
additional complications and may not be very easy for end users. Isn't
it enough to define HAVING to have a similar syntax to FILTER, but
restricted to variables that appear in the  AS clause? Ie, in the
example you have, one could then say

HAVING (?totalPrice > 10)

I am just looking at some simpler scheme that would cover our main use
cases, rather than completeness...

Ivan

Chimezie Ogbuji wrote:
> Thanks Andy.
> 
> I've extended the syntax to include a 'HAVING' expression.  I still need to
> reconcile the functions in the draft formulization with the algebraic
> operators in the previous section to determine the specific changes needed
> to support the semantics of HAVING.
> 
> The intuition, however, is for the Aggregation operator to take an
> additional argument that is the boolean expression to use as a selection
> criteria while performing the aggregation.  The expression will include
> references to aggregate functions that will be evaluated in the same way as
> the function(s) given in FuncAndVars, except their values aren't returned as
> bindings but rather are used to evaluate the expressions to determine which
> solution mappings are discarded
> 
> One outstanding issue with the grammar changes is that the PrimaryExpression
> used within HavingExpression would need to be different from the
> PrimaryExpression used elsewhere insofar as references to aggregate
> functions will need to be added to that part of the grammar.
> 
> -- Chimezie
> 
> 
> On 8/21/09 5:11 AM, "Seaborne, Andy" <andy.seaborne@hp.com> wrote:
> 
>> 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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> 
> 
> ===================================
> 
> P Please consider the environment before printing this e-mail
> 
> Cleveland Clinic is ranked one of the top hospitals
> in America by U.S. News & World Report (2008).  
> Visit us online at http://www.clevelandclinic.org for
> a complete listing of our services, staff and
> locations.
> 
> 
> Confidentiality Note:  This message is intended for use
> only by the individual or entity to which it is addressed
> and may contain information that is privileged,
> confidential, and exempt from disclosure under applicable
> law.  If the reader of this message is not the intended
> recipient or the employee or agent responsible for
> delivering the message to the intended recipient, you are
> hereby notified that any dissemination, distribution or
> copying of this communication is strictly prohibited.  If
> you have received this communication in error,  please
> contact the sender immediately and destroy the material in
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> 
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
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Received on Tuesday, 25 August 2009 10:35:11 GMT

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