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Duplicate columns and group keys

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Thu, 30 Sep 2010 11:57:27 +0100
Message-ID: <4CA46D17.301@epimorphics.com>
To: SPARQL Working Group <public-rdf-dawg@w3.org>
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
}

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

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 10:58:50 GMT

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