Efficient, Automatic Web Harvesting

There are two problems associated with conventional web crawling techniques: a crawler cannot know if all resources at a non-trivial web site have been discovered and crawled (“the counting problem”) and the human-readable format of the resources are not always suitable for machine processing (“the representation problem”). We introduce an approach that solves these two problems by implementing support for both the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) and MPEG-21 Digital Item Declaration Language (DIDL) into the web server itself. We present the Apache module “mod oai”, which can be used to address the counting problem by listing all valid URIs at a web server and efficiently discovering updates and additions on subsequent crawls. Our experiments indicated comparable performance for initial crawls, and dramatic increases in update speed mod oai can also be used to address the representation problem by providing “preservation ready” versions of web resources aggregated with their respective forensic metadata in MPEG-21 DIDL format.