Missing DocBook 4.1 ".gml" files

[Alejandro Pulver]

Hello,

When I run "nsgmls" over a DocBook 4.1 SGML file (specifying the catalog file: '-c /usr/local/share/sgml/docbook/4.1/catalog') it outputs the following messages:

---------- BEGIN ----------
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:54:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-amsa.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:61:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-amsb.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:68:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-amsc.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:75:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-amsn.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:82:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-amso.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:89:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-amsr.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:96:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-box.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:103:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-cyr1.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:110:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-cyr2.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:117:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-dia.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:124:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-grk1.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:131:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-grk2.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:138:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-grk3.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:145:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-grk4.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:152:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-lat1.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:159:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-lat2.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:166:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-num.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:173:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-pub.gml" (No such file or directory)
nsgmls:/usr/local/share/sgml/docbook/4.1/dbcent.mod:180:0:E: cannot open "/usr/local/share/sgml/docbook/4.1/iso-tech.gml" (No such file or directory)
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What are these files?
Where can I find them?

Thanks and Best Regards,
Ale