This class provides a couple of utilities for different use cases.
With the following command the uri in $uri will be compacted. That means that for instance http://www.w3.org/2000/01/rdf-schema# will replaced by rdfs:.
$uri = "http://www.w3.org/2000/01/rdf-schema#label";
$compactUri = OntoWiki_Utils::compactUri($uri);
// now $compactUri = "rdfs:label"