Property:Has uniqueness constraint

"Has uniqueness constraint" is a predefined property provided by Semantic MediaWiki to restrict value assignments for each instance to be unique (or one at most). Uniqueness is established when two values are not equal in their literal representation and any violation of that constraint will be categorized as error. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.