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Re: Duplicate columns and group keys

From: Lee Feigenbaum <lee@thefigtrees.net>
Date: Thu, 30 Sep 2010 08:51:28 -0400
Message-ID: <4CA487D0.4020407@thefigtrees.net>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
On 9/30/2010 6:57 AM, Andy Seaborne wrote:
> Following a jena-dev question, I wondered what do implementations do
> with the following?
>
> # Duplicate select variable - SPARQL 1.0
> SELECT ?s ?s ?p ?o
> {
> ?s ?p ?o
> }

Glitter returns the ?s "column" twice, including listing it twice in the 
<head> of the SRX.

> # Duplicate group by variable
> SELECT ?s
> {
> ?s ?p ?o
> } GROUP BY ?s ?s

I haven't tried this, but I'd expect this just works the same as GROUP 
BY ?s - is there a subtlety here that I'm missing?

Lee


> In result sets: two cases, the same binding duplicated in a row and an
> attempt to provide different bindings (the latter IMHO is an error
> because it's nonsensical in the design).
>
> # Duplicate in result set (XML) - SPARQL 1.0
> <?xml version="1.0"?>
> <sparql xmlns="http://www.w3.org/2005/sparql-results#">
> <head>
> <variable name="s"/>
> <variable name="p"/>
> <variable name="s"/>
> <variable name="o"/>
> </head>
> <results>
> <result>
> <binding name="s"> <!-- First -->
> <uri>http://example/s</uri>
> </binding>
> <binding name="p">
> <uri>http://example/p</uri>
> </binding>
> <binding name="s"> <!-- Second (here, the same value) -->
> <uri>http://example/s</uri>
> </binbding>
> <binding name="o">
> <uri>http://example/o</uri>
> </binding>
> </result>
> </results>
> </sparql>
>
> # Duplicate in result set (JSON) - SPARQL 1.0
> {
> "head": {
> "vars": [ "s" , "p" , "s" , "o" ]
> } ,
> "results": {
> "bindings": [
> {
> "s": { "type": "uri" , "value": "http://example/s" } , # First
> "p": { "type": "uri" , "value": "http://example/p" } ,
> "s": { "type": "uri" , "value": "http://example/s" } , # Second
> "o": { "type": "uri" , "value": "http://example/o" }
> }
> ]
> }
> }
>
> Andy
>
> Appendix: JSON and duplicate keys:
>
> The JSON description on json.org does not ban this
> [[
> An object is an unordered set of name/value pairs.
> ]]
>
> and RFC 4627
> [[
> An object is an unordered collection of zero or more name/value
> pairs, where a name is a string and a value is a string, number,
> boolean, null, object, or array.
> ...
> The names within an object SHOULD be unique.
> ]]
>
> which means ("x", 1) ("x", 2) is a legal as a set of two different pairs
> and ("x", 1) , ("x", 1) is a set of one pair but an unordered list or
> bag of two pairs.
>
> The org.json Java implementation throws an exception.
>
>
Received on Thursday, 30 September 2010 12:52:02 GMT

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