The structure of Wikidata – Wikidata Query Service Tutorial

Tabular vs. Linked Data

To learn how to use the Wikidata Query Service, you will first need to understand the structure of Wikidata, that is, what a database of linked data looks like.

In this tutorial, many examples will be based on the data presented in the following table:

Item ID	Title	Director	Duration	$Box office
wd:Q17738	Star Wars Episode IV: A New Hope	George Lucas	121	775398007
wd:Q181795	Star Wars Episode V: The Empire Strikes Back	Irvin Kershner	124	538400000
wd:Q181803	Star Wars Episode VI: Return of the Jedi	Richard Marquand	134	475100000
wd:Q165713	Star Wars: Episode I – The Phantom Menace	George Lucas	136	1027044677
wd:Q181069	Star Wars Episode II: Attack of the Clones	George Lucas	142	649398328
wd:Q42051	Star Wars: Episode III – Revenge of the Sith	George Lucas	140	848800000
wd:Q6074	Star Wars: The Force Awakens	J. J. Abrams	135	2068223624
wd:Q18486021	Star Wars: The Last Jedi	Rian Johnson	152	1332539889
wd:Q20977110	Star Wars: The Rise of Skywalker	J. J. Abrams	141	851058441

This is a small dataset that details some information about films in the Star Wars series. For each film, a few attributes or properties are shown: the title of the film, its director, its duration (in minutes), and the box office takings accumulated by the film (in dollars). If you are familiar with Excel or SQL, this way of presenting data should look familiar to you. However, Wikidata is not a database based on tables, like the one above, but rather has a “Linked Data” format. What does that mean?

In a linked data model, the data in the first row of the table above would be represented as:

In a linked data (or “graph”) view, the property (black lines) links the item (shown in blue) to the corresponding property value (shown in green).

Wikidata, which uses the linked data format, stores information in the form of statements. Statements, formally known as “subject, predicate, object” triples, have an Item-Property-Value structure.

For instance, the statement “The sky has the color blue” consists of:
(1) a subject (“the sky”)
(2) a predicate (“has the color”)
(3) an object (“blue”).
Likewise, the statement “Star Wars Episode IV: A New Hope was directed by George Lucas” consists of (1) a subject/Item “Star Wars Episode IV: A New Hope ”, (2) a predicate/Property “was directed by”, and (3) an object/Value “George Lucas”.

You can think of each row in the data table above as an Item, the column headers as Property names, and the data cells as property Values.

So another way of describing this data is through statements. For example, for the item in the first row of the table, the data can be described with the statements:

Item	Property	Value
Q17738	title	Star Wars Episode IV: A New Hope
Q17738	director	George Lucas
Q17738	duration	121 minutes
Q17738	box office	775398007

Statements describe detailed characteristics of an Item, and consist of property-value pairs, such as “director: George Lucas”, or “duration: 121 minutes”.
Properties in Wikidata have a P followed by a number. For example, the property “director” is P57.
The value of this property for the item Q17738 (Star Wars Episode IV: A New Hope) is George Lucas, which is also an item – Q38222.
Not all values are also items. For example, the value for the property “duration” (P2047) for the item Q17738 is 121 minutes.

Some properties might have values that aren’t items. As noted, for example, the value of the property “duration” (P2047) for the item Q17738 is “121 minutes”, which is a quantity. The value of “publication date” (P577) in the United States is “25 May 1977”, a date. Other data types frequently used are strings (a chain of characters, such as texts or codes), globe coordinates and monolingual texts ( a string that isn’t translated to other languages). Wikidata currently has 27 different data types, and you can find more information about them here.