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Roy, I don't think a gross statistical count is enough to let us know 
which fields are important, since some only apply to certain types of 
materials that occur less frequently (e.g. objects, archival materials, 
sheet music). So although a count is interesting, it's going to take 
some more semantic analysis.

As an example, one field that I would greatly miss is the 502 
Dissertation Note. Unless things have changed since I was still 
processing MARC records, the presence of this note is the only way to 
know that what you have is a dissertation. Obviously folks in academic 
libraries would want to be able to limit some searches to dissertations. 
(I'd be happy for "dissertation" to be a value somewhere in the future 
record -- although we'd still need the information that is in the note, 
and it might need some special treatment.)

Also, the sparsity of the obsolete fields in the 4XX area may be an 
OCLC-specific datum. My guess is that OCLC did automated cleanup of 
those fields. There may be many local catalogs that still have a 
significant number of records with those obsolete fields because they 
didn't have that capability.

In the end, we should be driven not by what is in MARC records today, 
and definitely not by how things look in one single (albeit large) 
bibliographic database. We need to be looking at use cases, and what 
services we wish to provide. Do we think someone is going to want to 
limit searches to dissertations? If so, that is information that helps 
us make decisions.

kc


On 1/28/13 9:49 AM, Tennant,Roy wrote:
> Could we please not make the mistake of thinking every field is worth the
> same? Of the fields below (see my report below), some do not appear at all
> within the WorldCat aggregation, whereas others appear a significant amount
> and a bunch are somewhere in between. If a tag only appears 33 times out of
> nearly 300 million MARC records, it likely isn't as important as one that
> appears over 50 million times. Just sayin'.
> Roy Tennant
> OCLC Research
>
> Out of 289,294,984 WorldCat records as of 1 January 2013:
>
> 016 (vital for Canadian libraries) - 50,439,937
> 055 (vital for Canadian libraries) - 3,201,913
> 060 (vital for medical libraries) - 2,190,698
> 070 (vital for agricultural libraries) - 1,069,479
> 080 (important for some European libraries) - 9,601,435
> OCLC's 090 - 12,166,182
> OCLC's 092 - 4,915,415
> 210 - 806,622
> 222 - 1,358,049
> 245$h - 79,201,026
> 247 - 242,964
> 264 - 53,586
> 336 - 198,637
> 337 - 199,079
> 338 - 140,598
> 440 - 2,852
> 400 - 33
> 410 - 9
> 411 - 0
> 503 (although obsolete, they exist in records) - 0
> 506 - 8,113,210
> 538 - 10,079,036
> 540 - 13,952,558
> 546 - 23,424,048
> 611 - 318,521
> 77X - multiple fields
> 78X - multiple fields
> 800 - 1,171,608
> 810 - 2,427,695
> 811 - 18,994
> 830 - 47,490,770
>
>
> On 1/27/13 1/27/13  5:19 PM, "J. McRee Elrod" <[log in to unmask]> wrote:
>
>>>   https://github.com/lcnetdev/marc2bibframe/blob/master/python/lib/marc.py.
>>> Anyone experiencing a sleepless night should consider this task :-).
>>
>> Again, interesting.
>>
>> Many MARC fields and subfields are not named, e.g.:
>>
>> All fixed fields
>> 016 (vital for Canadian libraries)
>> 055 (vital for Canadian libraries)
>> 060 (vital for medical libraries)
>> 070 (vital for agricultural libraries)
>> 080 (important for some European libraries)
>> OCLC's 090, 092
>> 210
>> 222
>> (but seldom used 243 is included)
>> 245$h
>> 247
>> 264
>> 336
>> 337
>> 338
>> 440, 400, 410, 411, 503 (although obsolete, they exist in records)
>> All 5XX notes seem undifferentiated except 505, 520, and 521, making a
>>    walk back to MARC impossible.
>> 506
>> 538
>> 540
>> 546
>> 611
>> 77X
>> 78X
>> 800
>> 810
>> 811
>> 830
>> etc.
>>
>> These missing fields are just those we have used, or often use,
>> without reference to MARC21 fields given in documentation, which are
>> *much* more extensive.
>>
>> So far, this seems a *very* dumbed down conversion, lacking information
>> important to our clients.
>>
>>
>>     __       __   J. McRee (Mac) Elrod ([log in to unmask])
>>    {__  |   /     Special Libraries Cataloguing   HTTP://www.slc.bc.ca/
>>    ___} |__ \__________________________________________________________
>>

-- 
Karen Coyle
[log in to unmask] http://kcoyle.net
ph: 1-510-540-7596
m: 1-510-435-8234
skype: kcoylenet