* @return a set of actual versions in bitset form
     */
    BitSet getSelectedVersions( String spec )
    {
        BitSet bs;
        if ( spec != null && spec.length()>0 )
            bs = convertVersions( spec );
        else
        {
            bs = new BitSet();
            for ( int i=1;i<=versions.size();i++ )
                bs.set( i );
        }
        return bs; 
    }