Help:Property constraints portal/Single value
|It is proposed that this informational page become a policy or guideline. Please see the discussion on its talk page or the project chat.
The following is a proposed Wikidata policy or guideline. The proposal may still be in development, under discussion, or in the process of gathering consensus for adoption.
single value constraint (Q19474404) specifies that a property generally only has a single value.
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).
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 values can be included and should not be removed. The most trustworthy value can be tagged with preferred rank, to allow data-reusers to get one value instead of getting multiple values. Statements that are backed up by sources that are believed to be incorrect should be tagged with deprecated rank.
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.