This is one of InLOC's direct properties.

A label is only mandatory in schemes and objects with no id. Otherwise they are optional.

If a label is given alongside an id, it should be a label for the resource identified by the id, and it should not introduce any information not implicit in the identified resource, as the id and label are intended to be machine and human readable equivalents. That is, any labels given should be human-readable names for the resource identified by the id property.

For any one subject, scheme or object instance, there should be no more than one label in any one human language, and no more than one without any specified language. If there is a label with no specified language, it should be taken as a default in language contexts where no label is given specifically for the context language.