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Re: query RDF dataset

From: Jitao Yang <jitao.yang@gmail.com>
Date: Tue, 2 Jun 2009 17:08:30 +0200
Message-ID: <eb1226bd0906020808g5f5c9733w499493cb6439e0b4@mail.gmail.com>
To: Yihong Ding <ding@cs.byu.edu>
Cc: semantic-web@w3.org, www-rdf-interest@w3.org
Dean Yihong,

Thank you very much for your advice for using UNION,
but in fact there is a difference between "?author dc:country ?country . "
and  "?author2 dc:country ?country2 ."
when I use it in the query.

On Tue, Jun 2, 2009 at 15:21, Yihong Ding <ding@cs.byu.edu> wrote:

> 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 15:09:33 GMT

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