<owl:FunctionalProperty>. . This means that it can have at most one value for each individual. It may have no values, but cannot have more than one. This characteristic has been referred to as having a unique property [W3C: http://www.w3.org/TR/owl-features]. For example, the has_ID property may be restricted as Functional. A reasoner may then deduce that no individual may have more than one ID. This type of restriction may be applied to both object and datatype properties (Figure 5.6).