Support converting GND authority file record

[nichtich]

GND records provided by the German National Library (e.g. http://d-nb.info/1020118989/about/marcxml) cannot be converted because:

• Field 008[11] is set to n (Not applicable) instead of z (Other)
• gnd is not specified in 040$f

The first may be fixed in mc2skos by also allowing n but the second needs to be done by German National Library.

After both changes (an example is included in https://github.com/gbv/mc2skos/blob/gnd/examples/gnd-1020118989.xml), the converted RDF contains an empty string triple:

skos:note ""@de ;

This should better be fixed in mc2skos.

Finally GND records contain mappings via field 024 to be converted too (#55).

[danmichaelo]

Do you understand why they use "n"? Seems a bit strange to me, but I'm not totally sure I understand the semantics of it :)

Are you in contact with DNB about adding 040$f? That would be good to have indeed.

[nichtich]

I got feedback, they are not going to change the date. Can we just accept n in 008[11] instead of rejecting the records? The connection to GND still needs to be given explicitly via --scheme and --uri:

 mc2skos --scheme http://d-nb.info/gnd/ --uri 'http://d-nb.info/gnd/{control_number}' examples/gnd-4003412-4.xml

I'd like to simplifiy this, e.g.

mc2skos --scheme gnd

To set a default value of 040$4 or 084$a.

[danmichaelo]

You didn't get an explanation as for why they prefer "n"?

The short form makes good sense, so I added support for that.