Citing URLs

Follow these guidelines when using URLs in your paper, based on the paper Persistence of Web References in Scientific Research, by Steve Lawrence, David N. Pennock, Gary William Flake, Robert Krovetz, Frans M. Coetzee, Eric Glover, Finn Arup Nielsen,Andries Kruger and C. Lee Giles in Computer, Feb. 2001. Additional remarks have been added in brackets.

For material not controlled by the author:

• Provide formal citations along with URL citations whenever possible, but include valuable URL citations even when formal citations are unavailable. The loss of some links over time is preferable to depriving readers of all links. Even when formal citations are available, providing an accompanying URL can significantly improve the information's accessibility.
• Provide enough context information so that readers can pose adequate search engine queries to track down invalid links. For example, when giving the URL for a preprint, provide the document's full title along with the full details of the authors - instead of, say, using "et al.".
• Check all URLs, particularly ones that have apparent embedded user information. It is best for somebody other than the author to check these URLs.

In case of URLs that cite repositories controlled by the author:

• Place material in a reliable central repository such as a preprint or software archive. This is particularly important for links to complete versions of papers, omitted proofs, and supporting data or results. [Most academic institutions have a technical report series. If one of the co-authors is a member of such an institution, strongly consider placing the full version of the paper there. For preprints, consider netlib.org. For open-source software, consider using the free services of sourceforge.net. Avoid using student accounts at all cost; use pointers to research lab or group pages, as they are often maintained even after the faculty or research staff person leaves an institution.]
• Name the repository and include the name in citations. This name is available for later searches. For software distributions, include a file with name of the software package; some search engine may index the filename. [Avoid storing just tar files, for example. At least store the manual page or README as a separate document to increase the likelihood that it will be indexed.] Provide a documented homepage for software and establish a domain name.
• When referencing software or software manuals, reference a URL for the entire project rather than URLs for specific software or manual versions. Version files frequently become unavailable after updating of the software or manual. [Also, you probably want readers to obtain the current release when they read the article, rather than the version available at the time the article was written.]
• Avoid URLs that depend on personal directory, specific machine or subnet name.