# Wikidata - What is it

Maher Asaad Baker

► To cite this version:

Maher Asaad Baker. Wikidata - What is it. 2021. hal-04636504

HAL Id: hal-04636504

https://ut3-toulouseinp.hal.science/hal-04636504v1

Preprint submitted on 6 Aug 2024

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# Wikidata - What is it

Maher Asaad Baker
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Wikidata is a wiki that is a database, a collaboratively edited multilingual knowledge graph hosted by the Wikimedia Foundation. It is the free knowledge base that anyone can edit. Just like Wikipedia, Wikidata is built on the MediaWiki wiki package which means that content on pages (just like this one!) can be added, modified, or deleted in collaboration with others. Unlike Wikipedia, Wikidata also uses Wikibase software which allows for collaborative editing of structured data.

In Wikidata, a concept, topic, or object is represented by an item. Each item is accorded its own page. A statement (Resource Description Framework (Q54872) graph format: Subject-Predicate-Object) is how the information we know about an item - the data we have about it - gets recorded in Wikidata. This happens by pairing a property with at least one value; this pair is at the heart of a statement. Statements can also be expanded on, annotated, or contextualized with additional values, as well as optional qualifiers, references, and ranks. Statements also serve to connect items to each other, resulting in a linked data structure.
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In Wikidata, items are used to represent all the things in human knowledge, including topics, concepts, and objects. For example, the "1988 Summer Olympics", "love", "Elvis Presley", and "gorilla" are all items in Wikidata.

There are a few important characteristics about items that contribute to the success of Wikidata:

## Notable items

Wikidata items are said to be notable. This means at least one of three things:

a corresponding page on a Wikimedia site such as Wikipedia, Wikivoyage, Wikisource, Wikiquote, Wikiversity, or Wikimedia Commons,
a clearly identifiable conceptual or material entity that
can be described using serious and publicly available
references or

The item fulfills a structural need. For more
information look at our notability policy.

Unique items

Items are also unique. Each item should represent a
clearly identifiable concept or object, or an instance of
a clearly identifiable concept or object. For example,
in Wikidata we can have items for both the concept of
planet (Q634) and an instance of a planet, Earth (Q2).

Linking items

Items can and should also be linked to each other.
Each item has a unique identifier (starting with a Q
prefix) and its own page in the Wikidata main
namespace. For example, for the items listed above,
1988 Summer Olympics (Q8470), love (Q316), Elvis
Presley (Q303) and Gorilla (Q36611) are the
respective item pages. These pages are where all the
data for each item is added, edited, and maintained,
mostly in the form of statements.

Properties

The property in a statement describes the data value,
and can be thought of as a category of data like
"color", "population," or "Commons media" (files
hosted on Wikimedia Commons). The value in the statement is the actual piece of data that describes the item.

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Each property in Wikidata is assigned a pre-defined data type which restricts what can be added as its value. For example, only other items can be added as a value for the property "color", only numbers can be added for the property "population," and only multimedia files viewable on Wikimedia Commons can be added for the property "Commons media."

## Values:

### 1 - Multiple values

If an item by nature can have properties with multiple values (like children of a person or official languages of a country), it is perfectly acceptable to add each of these multiple values.

If on the other hand an item ideally should have only one value (like the population of a city) but has multiple values (for example, because different sources report different numbers), all values may be added and additional qualifiers should be used.
Qualifiers are used to further describe or refine the
value of a property given in a statement.

## 2 - Unknown or no values

There are times when an item has either no value or
an unknown value for a given property. Depending on
the property, these data values still provide important
information about an item and should still be
recorded in Wikidata. For example, we could say that
Elizabeth I of England (Q7207) had no value for the
child (P40) property, which is quite different than not
recording anything at all. We could also say that
William Shakespeare (Q692) has an unknown value
for the date of birth (P569) property.

Unknown value may also mean the value is actually a
known object, but there's currently no Wikidata item
about the object. However, in this case it is strongly
recommended to create an item for the object, if it
meets the notability policy.

The majority of values in Wikidata will be custom
values, and are entered in the usual fashion. Unknown
values and no values are added to statements by
clicking on the icon beside the

## 3 - Item values

The most common kind of value on Wikidata is the
item. This means the property references another
item in Wikidata. For example you might have a
statement that says Albert Einstein (Q937) instance of
(P31) human (Q5). In other words the value of the
property instance of (P31) for Albert Einstein (Q937) is
the item human (Q5). If the value for the property
doesn't exist yet (say if Albert Einstein (Q937) were
some kind of alien) you can always just make a new
item.

4 - Quantitative values

When adding quantitative values the following
constraints should be noted. The largest positive
integer number that Wikidata allows is 9e124 and the
largest negative number -9e124. For floats one
additional decimal place is supported 9,9e124, but
9,91e124 is not possible. The smallest positive and
negative numbers are 1e-124 and -1e-124. For floats
the exponent can only be 123, making this the
smallest positive and negative floats: 1.0e-123 and -
1.0e-123 (Note that the zero will be preserved as an
indicator of the precision of the value. Compare this
to entering 1e-123).

Editing properties

Property entities can be edited like item entities with
labels, descriptions, aliases, and statements.

Property labels should be as unambiguous as possible
so that it is clear to a user which property is the correct
one to use when editing items and adding statements.
Properties rarely refer to commonly known concepts
but they are more constructs of the Wikidata with
specific meanings. Unlike items, property labels must
be unique.

Property descriptions are less relevant for
disambiguation but they should provide enough
information about the scope and context of the
property so that users understand appropriate usage
of the property without having to consult additional
help.

Property aliases should include all alternative ways of
referring to the property.

Example:

property: P161

label: cast member

description: actor performing live for a
camera or audience

aliases: film starring; actor; actress; starring

Label, description, and aliases of a property are first
discussed by the community during the property
proposal process. Major changes to a property should
be discussed on its talk page first.

Deleting properties

If you think a property should be removed from
Wikidata (for example, if is a duplicate of another
property in use), you will have to make a request for
its deletion.
Query service and other
improvements

On 7 September 2015, the Wikimedia Foundation announced the release of the Wikidata Query Service, which lets users run queries on the data contained in Wikidata. The service uses SPARQL as the query language. As of November 2018, there are at least 26 different tools that allow to query the data in different ways.

The Query Service is available at:

https://query.wikidata.org/

Below is a SPARQL example to search an instance of
(P31) television series (Q5398426) with main subject
(P921) about island (Q23442) and aviation accident
(Q744913). However similar results can also be found
directly on Wikipedia using category intersections if
the appropriate categories exist and are allowed.

SELECT ?item ?itemLabel

WHERE {

?item wdt:P31 wd:Q5398426.

?item wdt:P921 wd:Q23442.

?item wdt:P921 wd:Q744913.

SERVICE wikibase:label {bd:serviceParam
wikibase:language "[AUTO],en".}
}

Below is another SPARQL example to find an instance
of (P31) television series (Q5398426) where cast
member (P161) includes Daniel Dae Kim (Q299700)
and Jorge Garcia (Q264914). The television series
condition prevents displaying a television series
episode (Q21191270) / two-part episode
(Q21664088) and does not show results that are a film
(Q11424).

SELECT ?item ?itemLabel

WHERE {

?item wdt:P31 wd:Q5398426.

?item wdt:P161 wd:Q299700.

?item wdt:P161 wd:Q264914.

SERVICE wikibase:label {bd:serviceParam
wikibase:language "[AUTO here],en".}

}