At many instances, crawlers cannot retrieve or download all Web
services that exist on the Web. At some instances, service
providers may require authentication for clients to browse through
their service registries as in the case of the US Environmental
Protection Agency UDDI Registry in which access to the registry
is protected and controlled based on roles. However, this is
similar to situations in which Web crawlers attempt to crawl
secure content on the Web in which they must authenticate in
order to download Web pages within secured locations. Given this
fact, it is important for a Web services’ crawler to carefully select
and identify the sources and types of Web services and to retrieve
those that are considered important first so that the fraction of
Web services retrieved over the Web is more meaningful.