The Online Books Page

About Stable links

The Online Books Page is now offering stable links for its listings, as an alternative to direct links to online copies of books. You're welcome to use them in your own web pages and directories.

Following a stable link leads you to an information page on this site that describes the online book. This information page will also usually have one or more content links that go to the actual online book, wherever on the Internet that happens to be.

In our listings, the icon next to a book listing indicates the stable link. Click or select the icon to follow it.

What's useful about our stable links?

• They're less likely to stop working than many direct content links are
• They can be used to link to multiple copies of an online book that we list
• They give readers additional information about the book you're linking to
• They help readers find related titles.

While some web links stay valid for years and years, many become obsolete very quickly. Users who try to follow them get frustrated by seeing "not found" messages, or worse, instead of what they were looking for. And if you've made a link that goes bad, you'll have to hunt around for a new working link.

If you use our stable links, link rot becomes our problem, not yours. If we receive a bad link report for a book, we'll do our best to find another working content link to use from our stable link page. You don't have to change links on your end at all. In some cases, our stable link location may have content links to multiple copies of an online book, making it more likely that at least one of them will work at any given time.

Our stable links also put the book you're linking to in context, which can be very useful for readers. You can see information about the book such as its authors, subjects, and publication notes. You can follow hyperlinks from this information to find other books by the same author, with the same title, or on similar subjects, in our listings. Through these links, you have access not just to one book, but to many thousands of other books that might also be of interest.

How stable are these links, really?

We can't guarantee that all the stable links we give will provide access to a book forever. Because we're an index, not a repository, of online books, we do not control the actual content we link to. If all copies of a book are taken offline, we will no longer be able to give access to it. (And copyright holders generally have the legal right to withdraw their books.) Moreover, we might not notice bad content links in our own database right away (so please report them!), and we can't guarantee that this site will be around forever or always be in its current location.

On the other hand, we've maintained this site since 1993 (and have moved only once), and we give high priority to broken content link reports. So our links may well be stable enough for your purposes.

Here's the level of service we aim for:

• We try to investigate all broken link reports promptly; usually within 1 business day of receiving them. If we can find an alternative copy, we add a link to it, and remove the old content link if it's persistently bad.
• In some cases, new content links we provide may be to a slightly different edition of the same book. We consider that more useful to most users than simply delisting a book if we can't find the exact same edition online anywhere else. (If appropriate, the book's descriptive note will change accordingly.)
• If we can no longer find a suitable copy of the book on the Web, we replace our content links with a note that the book is delisted. We aim to keep that note available, and its associated stable link valid, for at least 1 year after "delisting".
• We will do our best to ensure that if our site ever moves or stops being maintained, the old stable links will continue to be available (though not necessarily updated) for at least 1 year, and will include prominent warnings about the pending obsolesence of the old stable links. In the case of a move, we intend to make all the stable links updatable with a simple pattern substitution (for example, substituting "example.com" for "onlinebooks.library.upenn.edu" in all links). The parts of the link that are unique to each book (generally the ID) should not change.

Alternatives

Some online book repositories we link to offer stable or persistent links of their own. You may want to look into these as well, and see whether those links or our stable links would meet your needs better.

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Edited by John Mark Ockerbloom (onlinebooks@pobox.upenn.edu)
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