http://www.geneontology.org/xml-dtd/08022001/go.dtd go.dtd
http://www.ncbi.nlm.nih.gov/entrez/query/DTD/pubmed_020114.dtd pubmed_020114.dtd

http://www.ncbi.nlm.nih.gov/entrez/query/DTD/nlmmedline_011101.dtd nlmmedline_011101.dtd
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http://www.ncbi.nlm.nih.gov/entrez/query/DTD/nlmmedlinecitation_011101.dtd nlmmedlinecitation_011101.dtd
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http://www.nlm.nih.gov/databases/dtd/nlmcommon_011101.dtd nlmcommon_011101.dtd