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Re: query RDF dataset

From: Yihong Ding <ding@cs.byu.edu>
Date: Tue, 2 Jun 2009 09:21:22 -0400
Message-ID: <8cbe5b450906020621o66fb8685u4358573d593e6c8f@mail.gmail.com>
To: Jitao Yang <jitao.yang@gmail.com>
Cc: semantic-web@w3.org, www-rdf-interest@w3.org
sorry, a typo.

there is not difference between "?author dc:country ?country . " or
"?author2 dc:country ?country2 ."



On Tue, Jun 2, 2009 at 9:19 AM, Yihong Ding <ding@cs.byu.edu> wrote:

> Jitao,
>
> I have not totally checked your query. My impression is, however, that you
> have made the query unnecessarily complex in its logic. You have claimed too
> many free variables for a fairly simple request. Therefore, the entire logic
> just becomes nearly untraceable. In analogy, what you have done is to have
> used a dozen of "no"s in a sentence; to the end, nearly nobody really knows
> whether you mean "no" or "yes".
>
> In particular, please also be aware that in RDF and SPARQL, there is no
> difference between when you say "?author dc:country ?country . " or ?bookURI
> dc:author ?author2 ." There are too many ambiguities in your query.
>
> Just rewrite your query in the following way.
>
> return: all the books which have no authors UNION all the books which have
> authors while every author must have its country be Italy
>
> good luck,
>
> yihong
>
>
>
>
>
>
> On Tue, Jun 2, 2009 at 3:51 AM, Jitao Yang <jitao.yang@gmail.com> wrote:
>
>> Dear all,
>>
>> if I have an RDF file like:
>>
>> <?xml version="1.0" encoding="utf-8"?>
>> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>>          xmlns:dc="http://purl.org/dc/elements/1.1/"
>>      xmlns:vcard="http://www.w3.org/2001/vcard-rdf/3.0#">
>>
>>     <rdf:Description rdf:about="http://example.org/BookJava">
>>         <vcard:fullname>Book Java</vcard:fullname>
>>         <dc:author>
>>             <rdf:Description rdf:about="
>> http://example.org/BookJava/authorA">
>>                  <dc:fullname>Bob Smith</dc:fullname>
>>                  <dc:country>Italy</dc:country>
>>              </rdf:Description>
>>         </dc:author>
>>         <dc:author>
>>             <rdf:Description rdf:about="
>> http://example.org/BookJava/authorB">
>>                  <dc:fullname>Tom Bush</dc:fullname>
>>                  <dc:country>Italy</dc:country>
>>             </rdf:Description>
>>         </dc:author>
>>     </rdf:Description>
>>
>>     <rdf:Description rdf:about="http://example.org/BookCpp">
>>         <vcard:fullname>Book Cpp</vcard:fullname>
>>         <dc:author>
>>             <rdf:Description rdf:about="
>> http://example.org/BookCpp/author2">
>>                  <dc:fullname>Mike Luck</dc:fullname>
>>                  <dc:country>France</dc:country>
>>             </rdf:Description>
>>         </dc:author>
>>         <dc:author>
>>             <rdf:Description rdf:about="
>> http://example.org/BookCpp/author1">
>>                  <dc:fullname>Alice Bird</dc:fullname>
>>                  <dc:country>Italy</dc:country>
>>             </rdf:Description>
>>         </dc:author>
>>         <dc:author>
>>             <rdf:Description rdf:about="
>> http://example.org/BookJava/authorB">
>>                  <dc:fullname>kobe Mc</dc:fullname>
>>                  <dc:country>Italy</dc:country>
>>              </rdf:Description>
>>         </dc:author>
>>     </rdf:Description>
>>
>>     <rdf:Description rdf:about="http://example.org/BookC">
>>         <vcard:fullname>Book C</vcard:fullname>
>>     </rdf:Description>
>>
>> </rdf:RDF>
>>
>> I want to query "the books whose authors are all Italian" or "the books
>> which have no authors",
>> so I use SPARQL like:
>>
>>             PREFIX dc:<http://purl.org/dc/elements/1.1/>
>>              PREFIX vcard:<http://www.w3.org/2001/vcard-rdf/3.0#>
>>             SELECT DISTINCT ?bookName
>>             WHERE {
>>                     ?bookURI vcard:fullname ?bookName .
>>                     OPTIONAL{
>>                             ?bookURI dc:author ?author .
>>                             ?author dc:country ?country .
>>                             FILTER(?country = \"Italy\") .
>>                             OPTIONAL{
>>                                     ?bookURI dc:author ?author2 .
>>                                     ?author2 dc:country ?country2 .
>>                                     FILTER(?country2 != \"Italy\")
>>                                     }
>>                             FILTER(bound(?country2))
>>                             }
>>                     FILTER(!bound(?author))
>>                   }
>>
>> I can get the right answers:
>> ---------------
>> | bookName    |
>> ===============
>> | "Book C"    |
>> | "Book Java" |
>> ---------------
>> but, my original idea is FILTER(!bound(?country2)) which means filter the
>> books which have non-Italian authors,
>> however if I use  FILTER(!bound(?country2)), it will return the opposite
>> answers:
>> --------------
>> | bookName   |
>> ==============
>> | "Book C"   |
>> | "Book Cpp" |
>> --------------
>> I can not understand the reasons?
>>
>> Thank you very much for your help to explain to me.
>>
>> Best wishes,
>> Jitao
>>
>
>
>
> --
> ===================================
> Yihong Ding
>
> http://yihongs-research.blogspot.com/
>



-- 
===================================
Yihong Ding

http://yihongs-research.blogspot.com/
Received on Tuesday, 2 June 2009 13:21:58 GMT

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