NOTE the attribute has cardinality [0..1] and is voidable, which means that: <ul> <li>in case the concept of grammatical number has no sense for a given name (i.e. the attribute is not applicable), the attribute should not be provided.</li> <li>in case the concept of grammatical number has some sense for the name but is unknown, the attribute should be provided but <i>void</i>.</li> </ul>