Help:Property constraints portal/Single value

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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.

If no constraint scope (P4680) is specified, this constraint is checked everywhere.

A qualifier can be defined as separator (P4155). This allows multiple values when using such qualifiers.

Possible actions[edit]

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).
  • If the violation is on a qualifier, it is possible that there should be two (or more) statements with one qualifier each, instead of one statement with two (or more) qualifiers using the same property. For instance, if a person received an award more than once, they should have several award received (P166) statements with one point in time (P585) qualifier each, not one award received (P166) statement with several point in time (P585) qualifiers. Likewise, a reference might need to be split up.
  • It is possible that a separator (P4155) (or several of them) should be defined for the constraint, to declare that multiple values are acceptable as long as they have certain different qualifiers.
  • If the constraint specifies a legal separator (P4155) (or a set of them), it is possible that such a qualifier should be added to a statement.
  • It’s possible that the item is a rare, but legitimate exception to the constraint, and nothing should be done.

Parameters[edit]

This constraint has one optional parameter:

separator (P4155)
Contains the separators. May contain one or more properties. If specified, multiple statements with the same value do not constitute a violation of this constraint as long as they have different qualifiers for the properties specified here.

Examples[edit]

Example 1[edit]

No parameter.

property constraint
Normal rank single value constraint Arbcom ru editing.svg edit
▼ 0 reference
+ add reference
+ add value

Example 2 - separator[edit]

With separator (P4155) parameter. For example, the capital (P36) may relocate to different place.

property constraint
Normal rank single value constraint Arbcom ru editing.svg edit
separator start time
end time
determination method
▼ 0 reference
+ add reference
+ add value

Template[edit]

When the constraint is set to the property, the following template is automatically displayed in the property talk page. The template is created by Module:Constraints using Template:Constraint, invoked from Template:Property documentation. Translations are defined at Module:i18n/constraints.

Single value: this property generally contains a single value. (Help)
Exceptions are possible as rare values may exist.
List of this constraint violations: Database reports/Constraint violations/P19#Single value, SPARQL, SPARQL (new)

Lists[edit]

Lists of properties which are set single value constraint.