The Life and Death of URLs: The Case of Journal of the Medical Library Association
Isfandyari-Moghaddam, Alireza, Saberi, Mohammad-Karim, Library Philosophy and Practice
The use of Internet for identifying valuable and timely information has become inevitable for most scientists as well as the public with access to the World Wide Web, since scientific and other work is created and added in digital format on the Internet every day (Falagas et al., 2008). Therefore, the use of Web links or citations has become common in journal papers, conference articles and other scholarly publications (Goh and Ng, 2007).
Despite the popularity of Web citations, we still may question the integrity of this practice. How often have we tried to link to URLs only to find a "404 Not Found" or other messages denying access? These warnings let us know that the information we came to access is no longer accessible at this site. The information may have been moved to another site, equipment may be down, or the information may have been removed completely (Germain, 2000). As a result, it should be accepted that due to ever-changing, instable and temporal identity of the Internet, Web citations (URLs) are exposed to the risk of decay. In a word, they disappear easily.
A common measure of URL decay is the half-life, defined as the period of time required for half of a defined Web literature to disappear (Koehler, 2004; Goh and Ng, 2007). Using this measure, several studies to date have dealt with this general problem of "URL decay". In order to make a better comparison between results of the present study and previous ones, here in the form of Table 1, we can have a look at them.
This article aims to examine URL decay of articles published in JMLA. Because JMLA is a freely available--according to DOAJ  (2008), it is among 3563 open access journals--international and scholarly journal, indexed in ISI, it was chosen to study. To collect related information, all issues (28 ones) of JMLA from 2002 to 2008 (a relatively seven-year time) were extracted. It should be noted that only articles which had references have been studied. Accordingly, Editorial, Case Study, Brief Communications, Special Report, Book Reviews, Electronic Resources Reviews and so on which had no references have been neglected. Consequently, 231 articles have been identified. Among them, articles which had Web citations were selected as research population. Afterwards, all URLs were extracted from these articles. Finally, in order to examine URLs decay, availability of individual cited URLs was scanned. Results of these tests were then compiled and analyzed to examine reasons for failure as well as to obtain the half-life value of Web citations in JMLA.
In the present study, the Web resources referred to by authors in JMLA articles in the references section of their papers have been studied. A total number of 1049 Web citations (URLs), as obtained from the bibliographies of 231 papers, have been analyzed and the necessary interpretations were made.
Distribution of articles, citations and Web citations. As shown in Table 2, totally, 231 articles have been published in JMLA during years 2002-2008. It is important to note that year 2005 with 42 articles and year 2008 (the last year ofpublication ofJMLA) with 12 articles have the most and the least rate of articles, respectively. It should be reminded that only 2 issues of 2008 have been released when the study was in process. According to Table 2, of 231 published articles, 175 articles (76%) have Web citations. Moreover, there were total number of 1049 citations whether printed or Web citations in 231 articles, and average "5 Web citations" was calculated per paper.
The Decay and availability of URLs. Table 3 demonstrates that of 1049 cited URLs, 69% were accessible, while only 31% were inaccessible. In fact, decay rate (31%) in the present research is more than decay rate estimated by Dellavalle et al (2003) namely 13%. Also, our finding in relation to URL decay is fully compatible with Goh and Ng' results (Goh and Ng, 2007). …