Complex sentence: One relatively straightforward measure is the "Web Impact Factor" (WIF) defined by Ingwersen in 1998 as the number of total link pages, divided by the number of web pages published in the site that are accessible to the crawler.
Split into simpler sentences: One relatively straightforward measure is the "Web Impact Factor" (WIF) introduced by Ingwersen (1998). The WIF measure may be defined as the number of web pages in a web site receiving links from other web sites, divided by the number of web pages published in the site that are accessible to the crawler.