This class implements Cocoon's org.apache.cocoon.caching.CacheValidity interface.

His functionality is to check for pages which are externaled controled by the External Cache Invalidator Server.

When a page is served by DBPrismGenerator and it includes the special sitemap argument Cache-Control equal to External a instance of this class is returned to control future request to this page. Every new request for the same page will be checked by this instance against the External Cache Invalidator Server, if the page is no longer valid (Externally invalidated by the user) this object will return false and Cocoon will call again to DBPrismGenerator for a new page.