omitting SPARQL prefixes

Hi guys I would like to know if I can have a blank prefixes for most of one
resources at same time. The way that I did doesn't work. It always gets the
last prefix with the same name.

Can someone help me?

 String sparqlQueryString = " PREFIX : <http://dbpedia.org/ontology/> "
                              + " PREFIX : <http://dbpedia.org/property/> "
                              + " PREFIX : <http://dbpedia.org/resource/> "
                              + " SELECT ?abstract WHERE "
                              +" { :Dilma_Rousseff :birthName ?abstract . }
";

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Phd. in Computer Science