Empirical Observations Regarding Predictability in User Access-Behavior in a Distributed Digital Library System

Today document archives are geographically distributed but often not replicated. This can potentially result in a low quality of service in terms of reduced availability and long user-perceived access times. Instead of indiscriminate replication we study the effectiveness of caching techniques such as prefetching and selective preloading. Our technique analyzes whether user access behavior is predictable enough to guess what articles to prefetch or to preload based on access logs from DADS, a digital library system for scientific journal articles developed at DTV, the Technical Knowledge Center of Denmark. We have found that once a literature search has been narrowed to up to ten articles, there is a high likelihood that some of them will be eventually downloaded. This suggests that prefetching can be used to hide the article transfer latency. We have also found that 80% of the article downloads are confined to less than 20% of the journals, so preloading a small fraction of the digital library database could significantly shorten the access latency and improve the availability.