One of my colleagues has forwarded me a set of messages from the Koha list about the use of MARC fields for various kinds of local data and asked if someone at OCLC might be able to comment and make some suggestions. I'll try to do that. If I understand correctly, the original proposal was to use field 090 based on the MARC format convention that any tag that contains a 9 in any position can be locally defined. It is true that this is one of the fundamental conventions of MARC tagging (for both MARC 21 and UNIMARC) but, as always, there are some exceptions. One is field 490 (Series statement). That field was part of the USMARC format before the convention about tags with 9 was established and it continues to be defined in MARC 21 and is, thus, not available for local definition. Another exception is field 090. That field used to be defined in USMARC but was made obsolete in 1982 when the whole block of 09X fields were designated for local use and definition. Another of the underlying principles of the MARC format is that obsolete fields should not be reused for different purposes since existing records may continue to contain the obsolete fields. That's part of the reason, I believe, that several comments that I read suggested that field 090 was not a good choice. All of us in the MARC format world (libraries, local system vendors and utilities) have made use of various fields in the 9XX block, which is reserved for local use and definition in both MARC 21 (and its predecessor formats USMARC, CANMARC and UK MARC) so that raises some potential stumbling blocks in sharing data and defining fields for local use. For example, in both CANMARC and UK MARC, some of the 9XX fields (900, 910, 911, and 945 in UK MARC and 900, 910, 911, 930, 980, 981, 982, 983, and 990 in CANMARC) have in the past been used to embed authority cross references in bibliographic records. In addition, OCLC has either used itself or has verified that local systems have used the following additional 9XX fields: 901-907, 920-921, 935-936, 938-942, 944-953, 955-956, 961-962, 964-969, 971, 981-984, 987, 992, 994, 996 and 999. Amazingly enough, that does leave field 970 (one of the ones mentioned in the messages I saw) as available so that may be a good choice. I have also checked with one of my colleagues who knows more about UNIMARC than I do. He is not aware of any similar list of UNIMARC 9XX fields that have already been used for some purpose. I hope that this information is of use in your discussions. Glenn Patton Director, WorldCat Content Management OCLC Online Computer Library Center, Inc. 6565 Frantz Rd. Dublin OH 43017-3395 Phone: +1.800.848.5878, ext. 6371 or +1.614.764.6371 Fax: +1.614.718.7187 Email: mailto:pattong@oclc.org