Including "no attempt to code" as an LOC thesaurus is bad news

Evergreen 2.2 includes new Authority Control Set functionality intended to allow the definition of locally defined authority control headings. The primary mechanism for determining which Control Set is used by any given authority record is to look at the thesaurus fixed field (mnemonic: Subj), which must be uniquely linked to a Control Set. Failing that (in the case of no thesaurus code at all), there is a backup mechanism: if the thesaurus value for the authority record is missing or not mapped to any configured Control Set then Evergreen will look at the first Main Entry (1xx) field in the record, and find a control set which uses this field. This is, obviously, not perfect, but for non-overlapping authority field schemes, it works very well.

However, the seed data for Evergreen currently includes the "no attempt to code" value of "|" in the set of thesauri that point to the LoC Control Set. This value ("|") is also the default value for the Subj fixed field. This means that the fallback mechanism is very likely never reached, and anything short of fully specifying an appropriate thesaurus code for any non-LoC authority record will run afoul of a similar outcome as the bib-data loss situation described in bug #983487.

We can avoid this situation in most cases by /not/ tying the "|" thesaurus value to the LoC control set.

The attached branch accomplishes this goal by allowing the Control Set for a thesaurus to be NULL, removing the Control Set for "|" and removing the Control Set recorded for records with "|" as the thesaurus value, forcing Main Entry inspection on any use of the authority record where Control Set is required.

http://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/miker/auth-control-set-safety