Something unusual happened yesterday. I was asking a question in another SE, and had searched, in another browser tab, the Library of Congress (LoC) for the book title, programming the Z80. As I was typing my question, I heard a beep but did not know what it was. Later I needed to reference my search, switched to the proper tab, and the search results were gone. They had been replaced by the Online Catalog home page. I re-performed the same search, got my information, and went back to the SE tab to finish the question.
Soon, maybe 3 minutes later, I heard the beep again. Now that I knew something was happening with the LoC search page I went back to that tab. It had a requester up, counting down from 120, with two options, [Refresh Session] and [New Session]. Not responding within 120 seconds caused the tab to auto-forward to the home page. I had no idea why it wanted me to make a session choice, since I had never explicitly opened a session to begin with.
Why would the LoC keep the search page live? Why would it expire? It wouldn't reduce web traffic; in my case it actually increased it. The only reason I can think of is they are concerned with the search being current. Who knows, maybe a new book just got cataloged that would have met my search criteria.
My first search at the LoC failed. I was using the Library of Congress Card Number from the book, "78-73741". (These are now called Library of Congress Catalog Number, or LCCN.) However, the format of an LCCN has changed since then:
- Begin with year of publication. From 1898 to 2000, use the last two digits. The overlap years of 1898, 1899, and 1900 can be identified by the size of the serial number. From 2001 on, use four digits.
- The dash following year is optional, and the LoC now recommends to publishers that they leave it out.
- The serial number is 6-digits, 0-filled to the left (except apparently for books published between 1898 and 1900).
If you know the LCCN, a search is not even necessary. There is a direct URL for every book. In my case it is lccn.loc.gov/78073741 (with or without a dash following year). These pages expire as well, with the same session requester.