//unlinked prefix
if(context.getReference()==XturtlePackage.Literals.QNAME_REF__PREFIX){
return new DiagnosticMessage("no @prefix-Definition for "+linkText+" up to this point", Severity.ERROR, XturtleJavaValidator.UNKNOWN_PREFIX,linkText);
}
Severity severity=null;
if(object instanceof UriRef){
severity= levels.getUnresolvedUriRefLevel();
} else if(object instanceof QNameRef){
//if the prefix is unknown the qualified name will be null
//an unresolved prefix is dealt with separately