What do you do with open ended subject dates, when the Library of Congress has created authorities with closed dates and no open ended see references? This was the question we sought to answer over the last week.
Take for example, you have a bib record with the following heading:
650 _0 $aWorld politics$y1955-
The authority for this heading has the following authorized and see references:
sh 85148226
150 _0 $aWorld politics$y1955-1965
Although these records are related, in an automated process they wont be linked, and the ending date will not be supplied. We decided there had to be a better way to link these up, and the process wasn’t very difficult, in fact, we’ve been doing it for names forever!
The answer is in the hierarchy. If we allowed our hierarchy system to include the closing date for subjects, we could provide the open ended bib dates a form of hierarchy to match against.
In essence, our Authority record above would create 2 possible heading matches. They would be (after following our normalization routine):
$aWORLD POLITICS$1955-1965
$aWORLD POLITICS$1955-
Now your bib heading $aWorld politics$y1955- could match and update against the proper LC Authority record. When we started researching this, we discovered another caveat. In some cases there are 2 authorities, one with an open ended date and one with a closed date. Our conclusion is that it’s obviously better in this case to trust what the original cataloger selected and match the open ended authority, rather than the closed authority. An example of this would be the authorities:
sh 85007061
151_0$aArgentina$xPolitics and government$y1810-
sh 85007060
151_0$aArgentina$xPolitics and government$y1810-1817
In this case, our bib record heading of 651 _0 $aArgentina$xPolitics and government$y1810- would match the first Authority.
After figuring that out, we discovered a real surprise, headings that were exactly the same, but had different closing dates. For example, France — History — 1789 has the following Authorities:
sh 85051348
151_0$aFrance$xHistory$y1789-
sh 85051347
151_0$aFrance$xHistory$y1789-1900
sh 85051346
151_0$aFrance$xHistory$y1789-1815
sh 85051314
151_0$aFrance$xHistory$y1789-1793
Obviously there are different meanings for different time periods starting from 1789. Now, if the bib record had an open ended date, it would take the open ended authority. And, if the bib record had any of the closed dates, it would take the authority with the matching date.
Our focus here, has been making sure that open ended authorities take the best possible match, and if there are no open ended authorities, matching it to the correct closed date authority, without creating false positive results.