Property talk:P2021

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Erdős number
the "collaborative distance" between mathematician Paul Erdős and another person. Use point in time (P585) as qualifier and should be used with a source.

Represents	Erdős number (Q243972)
Data type	Quantity
Domain	human (Q5)
Allowed values	According to this template: integer ≥0 According to statements in the property: 0 ≤ 𝓧 ≤ not applicable1 ≤ 𝓧 ≤ 20 When possible, data should only be stored as statements
Allowed units	not applicable
Example	Paul Erdős (Q173746) → 0 Kevin Bacon (Q3454165) → not applicable Louis Ignarro (Q309820) → 10
Source	http://wwwp.oakland.edu/enp/ https://mathscinet.ams.org/mathscinet/freetools/collab-dist
Robot and gadget jobs	http://wwwp.oakland.edu/enp/thedata/
Tracking: usage	Category:Pages using Wikidata property P2021 (Q23909015)
Lists	Items with the most statements of this property Count of items by number of statements (chart) Items with the most statements Items with the fewest statements Count of items by number of sitelinks (chart) Items with the most sitelinks Items with the most sitelinks, but no link to one Wikipedia (sample: Welsh Wikipedia, cywiki) Items with the fewest sitelinks Most linked wikis Items with the most identifier properties Items with no other statements Most recently created items Items with novalue claims Items with unknown value claims Usage history (total) Usage history (main statement) Chart by item creation date Minimum and maximum Items with highest numeric value Items with lowest numeric value Map of people by place values: place of birth educated at work location residence place of death place of burial January 1st dates People with date of birth on January 1 People with date of death on January 1 People with both dates on January 1 Database reports/Humans with missing claims/P2021 Database reports/Constraint violations/P2021 Map Random list
Proposal discussion	Proposal discussion
Current uses	Total 2,468 Main statement 2,466 >99.9% of uses Qualifier 2 <0.1% of uses

[create Create a translatable help page (preferably in English) for this property to be included here]

Range from “0” to “+∞”: values should be in the range from “0” to “+∞”. (Help)

List of violations of this constraint: Database reports/Constraint violations/P2021#Range, hourly updated report

Range from “1” to “20”: values should be in the range from “1” to “20”. (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303). Known exceptions: Paul Erdős (Q173746)
List of violations of this constraint: Database reports/Constraint violations/P2021#Range

Units: “novalue”: value unit must be one of listed. (Help)

List of violations of this constraint: Database reports/Constraint violations/P2021#Units, hourly updated report

Conflicts with “subclass of (P279)”: this property must not be used with the listed properties and values. (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#Conflicts with P279, SPARQL

Type “human (Q5)”: item must contain property “instance of (P31)” with classes “human (Q5)” or their subclasses (defined using subclass of (P279)). (Help)

List of violations of this constraint: Database reports/Constraint violations/P2021#Type Q5, hourly updated report, SPARQL

Single best value: this property generally contains a single value. If there are several, one would have preferred rank (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#single best value, SPARQL

Item “sex or gender (P21)”: Items with this property should also have “sex or gender (P21)”. (Help)

List of violations of this constraint: Database reports/Constraint violations/P2021#Item P21, hourly updated report, SPARQL

Item “date of birth (P569)”: Items with this property should also have “date of birth (P569)”. (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#Item P569, SPARQL

Item “place of birth (P19)”: Items with this property should also have “place of birth (P19)”. (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#Item P19, SPARQL

Required qualifier “point in time (P585)”: this property should be used with the listed qualifier. (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#mandatory qualifier, SPARQL

Integer: values should be integers (ie. they shouldn't have a fractional part) (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#integer, SPARQL

Scope is as main value (Q54828448): the property must be used by specified way only (Help)

List of violations of this constraint: Database reports/Constraint violations/P2021#Scope, hourly updated report, SPARQL

No bounds: values can't have any bounds (e.g. 1 not 1±0) (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#No Bounds, SPARQL

Allowed entity types are Wikibase item (Q29934200): the property may only be used on a certain entity type (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P2021#Entity types

This property is being used by: ro:Format:Infocaseta Om de știință Please notify projects that use this property before big changes (renaming, deletion, merge with another property, etc.)

#Histogram of number of persons having specific Erdős number
SELECT ?value (COUNT(?value) AS ?count)
{
  ?item wdt:P2021 ?value .
#    BIND(strlen(STR(ROUND(?value))) as ?length)
#    BIND(IF(?quantityvalue<1,"<1",?length)   as ?scale)
}
GROUP BY ?value
ORDER BY ?value

Try it!