Out dated URLs (17/10/2002). There is now much printed literature in the public domain that makes reference to URLs (Uniform Resource Locators - Links to you and me). I like finding URLs in articles and technical papers as it means I can find more information on the subject I am reading. However I get wound up when that link is no longer valid! This is a permanent problem on the internet as it is constantly evolving and changing. Another problem is that authors usually list contact email addresses which can go out of date when they move between organisations. I don't have a perfect solution for these problems, but as search engines are now so powerful, if pages are moved they could contain a reference to old URLs where they were previously available, or an authors online CV/contact details could contain a list of his old email addresses so that he could be tracked down. This problem is especially problematic in journals and conference proceedings which are normally referenced and cited for many years after their publication.
Update (10/6/2003). Every computer on the internet has a unique IP address which is made up from 4 numbers each in the range of 0-255 and is listed in the form A.B.C.D. Obviously there are many more documents in the world than there are computers - but could a similar identity number or code be produced which could be used to find a document with that unique reference - even if it was moved from one host to another? or just its location changed on a host?