Wikidata

Wikidata is a collaboratively edited multilingual knowledge base hosted by the Wikimedia Foundation. It is a common source of open data that Wikimedia projects such as Wikipedia can use, and anyone else, under a public domain license. The used data model is the Resource Description Framework. Wikidata is powered by the software Wikibase.

Items. Parts and Types


Wikidata is a document-oriented database, focused on items, which represent topics, concepts, or objects. Each item is identified by a unique number, prefixed with the letter Q, known as a "QID". This enables the basic information required to identify the topic that the item covers to be translated without favouring any language.

Examples of items include, , , and.

Item labels need not be unique. For example, there are two items named "Elvis Presley": represents the American singer and actor, and  represents his self-titled album.

But the label and the description text needs to be unique together. So, an Item is related with an unique identifier (QID). An identifier is linked to a pair: a label and a description, to dissolve any ambiguity.

Item types are general and lexemes.

Main Parts


Fundamentally, an item consists of:


 * Obligatorily, an identifier (the QID), related to a label and a description.
 * Optionally, multiple aliases and some number of statements (and their properties and values).

We are going to present them, from highest to lowest ones.

Statements


Statements are how any information known about an item is recorded in Wikidata. Formally, they consist of key-value pairs, which match a property (such as "author", or "publication date") with one or more entity values (such as "Sir Arthur Conan Doyle" or "1902"). For example, the informal English statement "milk is white" would be encoded by a statement pairing the property with the value  under the item.

Statements may map a property to more than one value. For example, the "occupation" property for Marie Curie could be linked with the values "physicist" and "chemist", to reflect the fact that she engaged in both occupations.

Values may take on many types including other Wikidata items, strings, numbers, or media files. Properties prescribe what types of values they may be paired with. For example, the property may only be paired with values of type "URL".

Property and value
A property describes the data value of a statement and can be thought of as a category of data, for example for the data value  or education for a person item.

As said, properties, when paired with values, form a statement in Wikidata. Values can include qualifiers.

The most used property is, that is used on more than 53,000,000 item pages.

Properties have their own pages on Wikidata and as an item can include several properties, this results in a linked data structure of pages, under the same statement.

Properties may also define more complex rules about their intended usage, termed constraints. For example, the property includes a "single value constraint", reflecting the reality that (typically) territories have only one capital city. Constraints are treated as testing alerts and hints, rather than inviolable rules.

Optionally, qualifiers can be used to refine the meaning of a statement by providing additional information that applies to the scope of the statement, within the values. For example, the property "population" could be modified with a qualifier such as "as of 2011". Values in the statements may also be annotated with references, pointing to a source backing up the statement's content.

Lexemes
In linguistics, a lexeme is a unit of lexical meaning. Similarly, Wikidata's lexemes are items with a structure that makes them more suitable to store lexicographical data. Besides storing the language to which the lexeme refers, they have a section for forms and a section for senses.

Development history
The creation of the project was funded by donations from the Allen Institute for Artificial Intelligence, the Gordon and Betty Moore Foundation, and Google, Inc., totaling €1.3 million. The development of the project is mainly driven by Wikimedia Deutschland and was originally split into three phases:
 * 1) Centralising interlanguage links – links between Wikipedia articles about the same topic in different languages.
 * 2) Providing a central place for infobox data for all Wikipedias.
 * 3) Creating and updating list articles based on data in Wikidata and linking to other Wikimedia sister projects, including Wikimeta and the own Wikidata (interwikilinks).

Initial rollout
Wikidata was launched on 29 October 2012 and was the first new project of the Wikimedia Foundation since 2006. At this time, only the centralization of language links was available. This enabled items to be created and filled with basic information: a label – a name or title, aliases – alternative terms for the label, a description, and links to articles about the topic in all the various language editions of Wikipedia (interwikipedia links).

Historically, a Wikipedia article would include a list of interlanguage links, being links to articles on the same topic in other editions of Wikipedia, if they existed. Initially, Wikidata was a self-contained repository of interlanguage links. Wikipedia language editions were still not able to access Wikidata, so they needed to continue to maintain their own lists of interlanguage links, mainly at the end of the articles' pages.

On 14 January 2013, the Hungarian Wikipedia became the first to enable the provision of interlanguage links via Wikidata. This functionality was extended to the Hebrew and Italian Wikipedias on 30 January, to the English Wikipedia on 13 February and to all other Wikipedias on 6 March. After no consensus was reached over a proposal to restrict the removal of language links from the English Wikipedia, the power to delete them from the English Wikipedia was granted to automatic editors (bots). On 23 September 2013, interlanguage links went live on Wikimedia Commons.

Statements and data access
On 4 February 2013, statements were introduced to Wikidata entries. The possible values for properties were initially limited to two data types (items and images on Wikimedia Commons), with more data types (such as coordinates and dates) to follow later. The first new type, string, was deployed on 6 March.

The ability for the various language editions of Wikipedia to access data from Wikidata was rolled out progressively between 27 March and 25 April 2013.

On 16 September 2015, Wikidata began allowing so-called arbitrary access, or access from a given Wikidata item to the properties of items not directly connected to it. For example, it became possible to read data about Germany from the Berlin article, which was not feasible before. On 27 April 2016 arbitrary access was activated on Wikimedia Commons.

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.

On the other hand, in Wiktionary lateral pane, has been included "Wikidata item" in Tools, to help to create a new item and links for new pages, specially when the item is only in English Wiktionary and wants to link to othe Wikimedia project, rather than to Wiktionaries in other languages.

Reception
In November 2014, Wikidata received the Open Data Publisher Award from the Open Data Institute “for sheer scale, and built-in openness”.

As of November 2018, Wikidata information is used in 58.4% of all English Wikipedia articles, mostly for external identifiers or coordinate locations. In aggregate, data from Wikidata is shown in 64% of all Wikipedias' pages, 93% of all Wikivoyage articles, 34% of all Wikiquotes', 32% of all Wikisources', and 27% of Wikimedia Commons'. Usage in other Wikimedia Foundation projects is testimonial.

As of November 2018, Wikidata's data is visualized by at least 20 other external tools and at least 100 papers have been published about Wikidata. Its importance has been recognized by numerous cultural institutions.

Logo
The bars on the logo contain the word "WIKI" encoded in Morse code.

Applications

 * Mwnci extension can import data from Wikidata to LibreOffice Calc spreadsheets.
 * There are (at October 2019) discussions about using QID items in relation to what are being called QID emoji.
 * Wiki Explorer - Android application to discover things around you and micro editing Wikidata