Re: Output type of SELECT query (was Example of filtering an RDF stream)

On 12/4/15 8:38 AM, Gray, Alasdair J G wrote:
>
>> On 4 Dec 2015, at 11:32, james anderson <james@dydra.com 
>> <mailto:james@dydra.com>> wrote:
>>
>>> On 2015-12-04, at 12:00, Robin Keskisärkkä <robin.keskisarkka@liu.se 
>>> <mailto:robin.keskisarkka@liu.se>> wrote:
>>>
>>> From: "Gray, Alasdair J G" <A.J.G.Gray@hw.ac.uk 
>>> <mailto:A.J.G.Gray@hw.ac.uk>>
>>> Date: Friday 4 December 2015 11:13
>>> To: Tara Athan <taraathan@gmail.com <mailto:taraathan@gmail.com>>
>>> Cc: "public-rsp@w3.org <mailto:public-rsp@w3.org>" 
>>> <public-rsp@w3.org <mailto:public-rsp@w3.org>>
>>> Subject: Re: Example of filtering an RDF stream
>>> Resent-From: <public-rsp@w3.org <mailto:public-rsp@w3.org>>
>>> Resent-Date: Friday 4 December 2015 11:14
>
> [snip]
>
>>>  1. What is the output type if we just have a SELECT clause?
>>>
>>
>> if you intend to produce a graph, ”just a select clause" is not adequate.
>
> This is the point of my question. What is the model type of the result 
> of a select query? Is it a stream of bindings?

*If we want to venture into this territory*, we could consider to have 
another type of stream, which is a SPARQL query result stream.

Let's consider a particular example:
SELECT ?s ?t
WHERE {
   {?g ex:observedAt ?t}
    GRAPH ?g {?s :hasDailyAverageTempC ?o .}
    FILTER ( ?o < '20'^^xsd:decimal ) .
}

We could view the query application as applying to each element of the 
input stream, creating for each application a set of solution mappings.

I have a few points of confusion:
* Would this stream be available for retransmission, or is it only 
intended for consumption by a local application?
* If intended for retransmission, what constraints would we put on the 
sequence of transmission (important in the case where the queries are 
applied asynchronously, so there is no guarantee, in the general case, 
that the query results become available for retransmission in the same 
order of the input sequence).

I don't think it would make sense to view the query application as 
applying to (the unified RDF dataset) the entire stream at once, as this 
would result in a potentially infinite set of solution mappings, with no 
clear foundation for a decomposition of this set for incremental 
retransmission.

Tara
>
> Alasdair
>
> Alasdair J G Gray
> Fellow of the Higher Education Academy
> Assistant Professor in Computer Science,
> School of Mathematical and Computer Sciences
> (Athena SWAN Bronze Award)
> Heriot-Watt University, Edinburgh UK.
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