code>rotterdam</code> and <code>rottrdm</code> are the same object although we didn’t select a pair <code>rotterdam -&gt; rottrdm</code>. So all names <code>rotterdam</code>, <code>rottrdam</code>, <code>rotterdm</code>, <code>rottrdm</code> and <code>rtterdam</code> are going to be in one class. When the number of misspelled names increases and when the number of actual town names increases, the likelihood that two names that do not belong to the same object are linked by a chain of pairs increases. This