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 They had been replaced by the Online Catalog home page.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:

  1. 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.
  2. The dash following year is optional, and the LoC now recommends to publishers that they leave it out.
  3. 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.

  • You can edit your question regarding LCCN rather leaving a paragraph that says something wrong followed by one that corrects it...
    – wogsland
    Mar 3, 2017 at 14:47
  • 1
    @wogsland You're right; that was a better idea. I edited it, and thank you.
    – RichF
    Mar 3, 2017 at 15:12

1 Answer 1


You see this on a number of sites and generally it is related to the underlying software technology powering the site. A number of libraries here in Australia have a similar feature on their online catalogues and according to them it relates to the software that powers the catalogues.

Basically what is happening is that when you connect to the online catalogue a new session is being created as a guest session (similar to if you entered a username and password attached to a guest account). This allows you to browse the catalogue without needing to log in, however it uses the same code as what supervises authenticated sessions for actual users. The timeout is a security feature that is inserted into the catalogue as generally the online catalogue is also used on shared computers in the library itself. This feature means that after 2 minutes of not being used if someone else where to go onto the catalogue computer it would have reset the session so that the new user couldn't access the previous users search record or patron profile.

As a side note a quick check of the html for the LoC online catalogue shows a common directory name of /vwebv. A check online shows that this exists in the HTML and/or link structure for a large number of library catalogues. Further searches indicate that this software was created by ExLibris which was acquired by ProQuest in 2015, and is used in some of the worlds largest libraries with the same feature enabled based on my testing.

Disclaimer: I am not in any way affiliated with LoC, ExLibris, or ProQuest and have come across all of this through my research.

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