Help:Property constraints portal/Single value
single value constraint (Q19474404) specifies that a property should only have a single value, i. e. that items should not have more than one statement with this property.
For example, many identifiers (ISNI (P213), Freebase ID (P646), …) would generally only have a single value, as well as many non-identifier properties like place of birth (P19) and place of death (P20).
However, if several identifiers apply to the same item, all should be included, not removed. If sources list several possible place of birth (P19) and place of death (P20), all can be included. If present neither should be removed.
There are several possible ways to address a violation of this constraint:
- It’s possible that one of the statements belongs to a different item (e. g., the ISNI (P213) of another person), and should be moved to the other item (which may need to be created).
- It’s possible that one of the statements is incorrect and should be set to deprecated rank (e.g. the place of birth (P19) is known, but frequently get mis-reported with the value present).
- It’s possible that the item is a rare, but legitimate exception to the constraint, and nothing should be done.
This constraint does not have any parameters.