Complex sentence: In an XML Topic Map (XTM), only a topic can have a name or play a role in an association: one may use an association to make an assertion about a topic, but one cannot directly make assertions about that assertion.
Split into simpler sentences: In an XML Topic Map (XTM), only a topic can have a name or play a role in an association. One may use an association to make an assertion about a topic, but one cannot directly make assertions about that assertion.