DBpedia Querying: Troubleshooting Composer Data in SPARQL

·May 04, 2021 07:13 PM

Milan Dojchinovski Jan Forberg Hi Milan and Jan - thank you for the lovely tutorial! I am playing around with querying dbpedia and using composers as a practice example. For example, pull composer, composition and premier date of composition for e.g. classical music (1750-1820). Examining the examples under OnlineAccess, some things that are confusing me:

1.
Filtering in the where cause with ?person dbo:birthPlace :Berlin . causes an error in https://dbpedia.org/sparql, namely, Undefined default namespace prefix at ':Berlin' before '.'. How would that clause be written correctly for the sparql endpoint?
2.
dbo:SoccerPlayer returns results, yet dbo:MusicComposer- although defined in the ontology - does not. I am assuming that means no content was tagged with MusicComposer? How could one then find music composers?

Thank you!

🙌1

9 comments

· Sorted by Oldest

Milan Dojchinovski
·
Hi Eszter S., let me try to help here

Milan Dojchinovski

for 1) try following:

SELECT ?person WHERE {
    ?person dbo:birthPlace <http://dbpedia.org/resource/Berlin> . 
}

or shorter version

SELECT ?person WHERE {
    ?person dbo:birthPlace dbr:Berlin . 
}

dbr is prefix for http://dbpedia.org/resource/

Milan Dojchinovski

as for 2) to pull composers and their compositions you can try following:

SELECT * WHERE {

    ?composer a dbo:Person .
    ?composer dct:subject dbc:18th-century_classical_composers .
    ?composition dbp:composer ?composer . 
}

Milan Dojchinovski
·
usually, to have a better coverage one would need to craft several queries, and then merge the results
Milan Dojchinovski
·
do you have a use case for DBpedia in the music domain? would be happy to assist further
Eszter S.
·
Thank you, Milan! The above really helped. The use case is just a personal project a friend and I are working on. He is creating a way to show what classical pieces premiered each day (as a way of suggesting what to listen to) and I am helping as a way to learn more about querying kgs. It just seemed like a small, easy, bit-sized way to get into kgs.... One last thing - do you know of a good resource that explains how to find the right resource / prefix for things?
Louis G.
·
I know of a good one in one direction: if you come across a prefix but don't know what it is, you can enter it in prefix.cc :) found that super helpful. Would also be interested in any resource to go the other way
Milan Dojchinovski
·
Eszter S. not sure what you mean by "find the right resource / prefix for things"... but the list of defined prefixes in the sparql endpoint can be found at https://dbpedia.org/sparql?help=nsdecl
👀1
Eszter S.
·
That is very helpful, thank you! I believe the issue I am having is figuring out all the names of things. Like, as you showed, there is a dbc:18th-century_classical_composers. Not knowing that, how would I discover it? Right now, it feels like there is no discernible pattern that can be applied to each new question. For example, I had tried to translate the SoccerPlayer example from the OpenAccess to composers. However, since dbo:MusicaComposer does not seem to be linked to much, that doesn't work.

Milan Dojchinovski
·
Hi Eszter S., let me try to help here

Milan Dojchinovski

for 1) try following:

SELECT ?person WHERE {
    ?person dbo:birthPlace <http://dbpedia.org/resource/Berlin> . 
}

or shorter version

SELECT ?person WHERE {
    ?person dbo:birthPlace dbr:Berlin . 
}

dbr is prefix for http://dbpedia.org/resource/

Milan Dojchinovski

as for 2) to pull composers and their compositions you can try following:

SELECT * WHERE {

    ?composer a dbo:Person .
    ?composer dct:subject dbc:18th-century_classical_composers .
    ?composition dbp:composer ?composer . 
}

Milan Dojchinovski
·
usually, to have a better coverage one would need to craft several queries, and then merge the results
Milan Dojchinovski
·
do you have a use case for DBpedia in the music domain? would be happy to assist further
Eszter S.
·
Thank you, Milan! The above really helped. The use case is just a personal project a friend and I are working on. He is creating a way to show what classical pieces premiered each day (as a way of suggesting what to listen to) and I am helping as a way to learn more about querying kgs. It just seemed like a small, easy, bit-sized way to get into kgs.... One last thing - do you know of a good resource that explains how to find the right resource / prefix for things?
Louis G.
·
I know of a good one in one direction: if you come across a prefix but don't know what it is, you can enter it in prefix.cc :) found that super helpful. Would also be interested in any resource to go the other way
Milan Dojchinovski
·
Eszter S. not sure what you mean by "find the right resource / prefix for things"... but the list of defined prefixes in the sparql endpoint can be found at https://dbpedia.org/sparql?help=nsdecl
👀1
Eszter S.
·
That is very helpful, thank you! I believe the issue I am having is figuring out all the names of things. Like, as you showed, there is a dbc:18th-century_classical_composers. Not knowing that, how would I discover it? Right now, it feels like there is no discernible pattern that can be applied to each new question. For example, I had tried to translate the SoccerPlayer example from the OpenAccess to composers. However, since dbo:MusicaComposer does not seem to be linked to much, that doesn't work.