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Elements of a statement, from item Q42

This glossary defines important Wikidata concepts and refers to more detailed information. See Wikidata:Introduction for a general introduction into Wikidata and the glossary guidelines for how to write and improve glossary entries.

Alias (also also known as) is an alternative name for an item or a property. The usual or most important name is the label. Aliases help people find an item even if they don’t search with the label. For example, the item Q2 has the label “Earth” and aliases such as “Tellus” and “Blue Planet”. It's a type of term.
Article placeholder is an extension to display stub articles and to start Wikipedia articles based on a view of Wikidata items. See mw:Extension:ArticlePlaceholder.
A badge is an optional marker that can be attached to a sitelink to another Wikimedia page. For instance, a sitelink can be marked to link to a "featured article" or to a "proofread" page.
Category item, template item and module item are Wikidata items with sitelinks to categories, templates, or modules on Wikimedia sites. When the last sitelink is deleted, these items are generally deleted (see Wikidata:Database reports/to delete).
Claim is a piece of data about the entity on the page where the claim appears. A claim consists of a property (such as location) and either a value (e.g., Germany) or one of the special cases "no value" and "unknown value". A claim can have qualifiers, such as temporal qualifiers saying that the claim is valid within a specific time frame. Compared to triples in the RDF data model, a claim uses a property to express the predicate of a triple and a value to express the object of a triple. Claims form part of statements on item pages, where they can be augmented with references and ranks. They can also occur on non-item data pages.
Commons (or Wikimedia Commons) is a Wikimedia project to store images, audio, video and other files. Wikibase includes three different datatypes to link from Wikidata to media files, geographic shapes and tabular data. Commons is adding statements to files as mediaentities.
Completeness is an assessment of available data with a measure for coverage. At Wikidata the presence of an item or statement does not imply that all similar items or statements are present. Wikibase does not include any completeness indicator. Quantity properties can be used to compare with available statements or items. Example: The item about states of the USA has a statement with quantity 50. One can compare that with the count of uses of the item. A few tools attempt to measure completeness. To some extent, property suggester and suggestion constraints indicate elements missing to complete items.
Complex constraint (or custom constraint) is a constraint defined by a freely chosen SPARQL query in a template on a property talk page.
Conflation is a type of error, usually on an item, where aspects of several distinct concepts are mixed together. For example, an item with the date of birth of one person and the occupation of another person with the same name.
Constraint is a rule for how a particular property should be used. For instance most identifiers should have only one value, so there is a single value constraint on them. A special kind are called complex constraints.
Constraint report can refer to a series of periodically updated pages for each property based on constraints or a special page for an individual item or other entity.
Cradle is an editing tool to create new Wikidata items based on a form with predefined properties and values.
Datatype (or propertyType) is an attribute of a property specifying the type and shape of the value in each claim. Each property is assigned a pre-defined datatype, which usually can not be changed. Not all values can be linked, as long as there are certain datatypes missing. Data types can only be defined by developers. See also Special:ListDatatypes for currently available datatypes. Data type does not directly specify how values are stored internally; this is specified by value type.
Data namespaces are namespaces for pages that hold Wikidata entities. The data namespaces in Wikidata are the main namespace for the Wikidata items, "Property:" for properties, and "Lexeme:" for lexemes.
Date (or time or timeValue) is a datatype for property values. It allows to enter dates in different precisions and enables date calculations in queries. Hour or minute precision isn't supported. The Wikidata property for the date of foundation has such values.
Description is a language-specific descriptive phrase for an item or property. It provides context for the label (for example, there are many items about places with the label "Cambridge"). The description therefore does not need to be unique, neither within a language or Wikidata in general, but it must be unique together with the label. Uniqueness for a combination of a label and a description is strictly enforced. If your edit does not meet this requirement you cannot publish it. It's a type of term.
Disambiguation item is a Wikidata item with sitelinks to disambiguation pages. This is its only purpose. Generally, it has a claim with instance of=Wikimedia disambiguation page.
Duplicate is an entity, generally an item, about the same concept as another entity. Duplicates are usually merged creating a redirecting entity. Special types of duplicates are temporary duplicates, permanent duplicates, and true duplicates.
Editing interface is a view that allows to add or modify data. These views are the default view, the Commons structured data interface, Wikidata bridge, and a series of API-based tools, notably QuickStatements, Cradle, PetScan, OpenRefine or the Pywikibot framework.
Entity is the content of a Wikidata page in one of the data namespaces, such as an item (in the main namespace), property (in the Property namespace) or lexeme (in Lexeme namespace). Every entity is uniquely identified by an entity ID, which is a number with a prefix; for example, starting with the prefix Q for an item and P for a property. An entity is also identified by a unique combination of label and description in each language. An entity may have alternate aliases in multiple languages (something similar to synonyms). Each entity has also a dereferenceable URI that follows the pattern where ID is its entity ID.

Other extensions may define new types of entities. For example:

Entity selector allows picking an entity by entering part of its name and selecting it from a list of search results. For items, the results are based on the labels and aliases. The description is displayed, if there is one. Example: type "human" to pick Q1156970 from "human (Q5) common name of Homo sapiens", "humanity (Q1156970) total world population of human", etc. This is different from the Property Suggester.
EntitySchema is a special type of Wikidata page containing a document in ShEx format, and related metadata. Although it may have labels, descriptions and aliases similar to items, it is not a type of entity. Entities may be validated against an EntitySchema using the ShEx2 — Simple Online Validator tool.
External identifier is a type of property — a string used in the database of external organizations. Some properties have external identifiers as values. They uniquely identify an item, although the uniqueness is not enforced by software, but controlled by constraint. For example, an ISBN for a book or the unique part of the URL of a movie or an actor in the Internet Movie Database.
Federation query is a query through a service available on Query Server allowing to access databases other than Wikidata.
Form is a string of characters that occurs in a particular grammatical context for a lexeme. Every Lexeme may have multiple forms. Forms are identified on each lexeme by the Lexeme ID followed by a dash, the letter "F" and a number. Forms may have statements just as other entities do. They are also assigned grammatical features such as "plural" for Form L1298-F2 ("forms").
Historic information is included by qualifying it with a date. If information is no longer current, date qualifiers are added instead of statements overwritten. Historic information is different from incorrect information
Human (or instance of human) is a Wikidata item about a person or an individual. It has a claim with instance of=human.
Incorrect information is a claim supported by a reference, but generally considered invalid or inaccurate. While Wikipedia generally excludes such information, Wikidata's deprecated rank allows to flag such statements. This helps avoid a situation in which it's deleted and erroneously re-added as valid information. Incorrect information is different from historic information
Instance of, subclass of, and has part (also class or type) are used on Wikidata to refer to the properties instance of, subclass of, has part(s), and a few other related ontological properties, their values, or items using them.
Item refers to a real-world object, concept, or event that is given an identifier (an equivalent of a name) in Wikidata together with information about it. Each item has a corresponding wiki page in the Wikidata main namespace. That page's title is the item's unique prefixed id, such as Q42. Every item may have human-readable labels and descriptions in multiple languages, but they are not necessarily unique. Items may also have aliases to ease lookup. The main data part of an item is the list of statements about the item. An item can be viewed as the subject-part of a triple in linked data.
Item identifier: see QID below.
Label (also name) is the main name given to an entity (i.e. an item or a property). E.g. the item with the item identifier Q7378 has the English label “elephant”. An entity may have one label in each given human language. Labels do not need to be unique. Descriptions and aliases are used to distinguish between entities with the same label. A label of a Wikidata page is automatically displayed in the user interface language in front of its id (e.g. "elephant (Q7378)"). A label does not uniquely identify the page; this function is served by its QID (title) only. The label is a type of term. In English, labels should generally follow the English language capitalization rules, i.e. uppercase should only be used in proper nouns.
Lag or database lag at Wikidata is a delay in the update of data on other projects or Query Server.
Language attributes are the language-specific labels, aliases and descriptions that are assigned to items, properties and queries. These are human-readable text to improve understanding of the scope of the item; for example, the specific type of real world entity. If they are missing, some of them can be replaced by strings from alternate languages, following the language fallback chains.
Language code is an identifier for the language of a label, description, alias, or monolingual text value. The language codes for labels, descriptions, and aliases are shared with other Wikimedia projects. More codes for monolingual text are defined specifically for Wikidata. Lexemes use some of these, as well as some additional codes or items to identify the language in lemma, gloss, and form. A language code is also assigned to sitelinks. Codes are based mostly on IETF language tags.
Language fallbacks (also language chains) are methods to systematically replace missing language attributes with strings from alternate languages. The exact replacement rules can be chosen depending on the type of page, whether the user is logged in, or the user preferred languages.
Lexeme is an entity of Lexicographical data. It contains sense and form sub-entities, but no sitelinks. Instead of a label, a description, and aliases, lexeme entities have a lemma (possibly more than one, for languages with spelling variants), a language, and a lexical category.
LID (or L number) The identifier for a lexeme entity in Wikidata, comprising the letter "L" followed by one or more digits.
Listeria (or Wikidata list) is a tool to show data from Wikidata in list form at Wikimedia projects. Data is periodically updated by bot.
Mainspace is one of the namespaces in a wiki. Namespaces in Wikidata other than the mainspace have prefixes. In Wikidata, the mainspace contains the pages with the items.
MediaWiki is the software that runs Wikidata, Wikipedia and other wikis. The MediaWiki installation of Wikidata makes use of the Wikibase extension. What is MediaWiki?
MediaInfo is a type of entity used to describe files. It's activated on Wikimedia Commons.
Meta pages These are all pages that are not entities, i.e. do not belong to the data namespaces. Wikidata meta pages contain unstructured content in wikitext, including Wikidata client side inclusion code. Examples are talk pages, category pages, project pages (in the Wikidata namespace) and help pages (in the Help namespace). Meta pages also comprise content and data automatically generated by the MediaWiki software (for example, the edit history of a page, or special pages).
Name item is a Wikidata item about a given name or a family name. Such items are used as values for family name or given name and can include additional information and sitelinks.
Namespaces are a kind of category for pages in a wiki. For each namespace you may have different rules about the pages and their content. In Wikidata, the most important namespace (or ‘main namespace’) is for the Wikidata items. The URL of a Wikidata mainspace page ends with a Q and a number, for example, Q7378 for “Elephant”. The pages in other namespaces start with the namespace name, the “prefix”. For example, help pages start with “Help:”, such as Help:Contents.
Object See Subject
Order of statements is generally determined by the view being used and not significant. Many views display data retrieved or entered first before other. Some views sort or allow to sort statements based on qualifier value, statement value, property, or datatype.
Page is an internal or external webpage with a unique title, for example, an article in Wikipedia main namespace or an item in Wikidata main namespace. A page is a part of a site. In Wikidata, the term "page" may refer to an item or a property page in the data namespaces, to a meta page in other namespaces, or to an external linked page on Wikipedia, another Wikimedia site, or an external site. A page on a client site may be referenced using a sitelink. Pages in the main namespace of Wikidata contain items, and one page can only hold one item.
Predicate See Subject
Prefix Used in the query service.
Project is a term often used in the Wikimedia movement to refer to a Wikimedia wiki. In Wikidata, the term usually refers to Wikidata itself.
Property describes the data value of a statement and can be thought of as a category of data, for example, "color" for the data value "blue". Properties, when paired with values, form a statement in Wikidata. Properties are also used in qualifiers. Properties have their own pages on Wikidata and are connected to items, resulting in a linked data structure.
Property suggester provides a preselection of properties when adding statements to Wikidata items. These are based on the frequency of the properties on similar items. Example: on an item with instance of=human only, suggestions could be sex or gender, occupation, date of birth. These may or may not be appropriate for the specific item. This is different from entity selector and suggestion constraints.
QID (or Q number) is the unique identifier of a data item on Wikidata, comprising the letter "Q" followed by one or more digits. It is used to help people and machines understand the difference between items with the same or similar names. For example, there are several places in the world called London and many people called James Smith. This number appears next to the label at the top of each Wikidata item.
Qualifier is a part of the claim that says something about the specific claim, often in a descriptive way. A qualifier might be a term according to a specific vocabulary but can also be a variant descriptive phrase (whether those terms or phrases are free text or part of some vocabulary would probably be up to the Wikidata community).
Quantity (incorrectly number) is a datatype for property values. It allows to enter integers or decimal numbers. Optionally a unit or a bound can be included. The Wikidata property for population has such values. Numeric identifiers are not quantities, but external identifiers.
Query is a search across items in Wikidata and their associated data. Queries are usually executed on the Wikidata Query Service using the SPARQL query language.
QuickStatements (QS) is a third-party tool that can edit Wikidata items, based on a simple set of text commands. The tool can add and remove statements, labels, descriptions, and aliases. It can also add statements with optional qualifiers and sources.
Rank is a quality factor used for simple selection and filtering in cases where there are several statements for a given property. In such cases, you may want to indicate which statement is more important or relevant than other statements. By default, a statement has the rank "normal", but you can change this to either "preferred" or "deprecated". "deprecated" rank can be used for statements supported by a reference, but considered incorrect.
Redirecting entity (or redirect) is an item or a lexeme that redirects to another item or lexeme (target). As in many uses these would need to be queried specifically, a bot usually replaces redirects used as values with their target.
A Reference (or source) is used to point to a specific resource that supports a claim in Wikidata. A reference can be a link to a URL or an item; for example, an item about a book. Wikidata does not aim to answer the question of whether a claim is correct, but only whether the claim appears in a reference. A claim together with the reference form a statement.
Repurposing is changing the definition or scope of an entity, in general an item, by editing its label, description or statements. Generally to be avoided.
Sandbox or sandbox items are series of items, properties and other entities at Wikidata to test features within the Wikidata live database. Examples: item Q4115189, property Property:P369, EntitySchema EntitySchema:E123, lexeme Lexeme:L123.
Sense refers to a specific meaning for a lexeme. Senses are identified on each lexeme by the Lexeme ID followed by a dash, the letter "S" and a number. Senses may have statements just as other entities do. They also allow a "gloss": a free-form description of the meaning (one per language).
Site is a reference to an external website in general, but in sitelinks it refers to specific registered wikis, for example, a Wikipedia language version. Those sites are referenced by site identifiers, or for short siteids, technically corresponding to the wiki's DBname. For example, the Latin Wikipedia's siteid is lawiki. Each external page can have only one link registered in Wikidata and one item can only have one link to each external site.
Sitelink is an identification of a linked page on another site. It consists of a site identifier and a title, and is stored in individual items in Wikidata. Sitelinks are used both for identifying an item from an external site, and as a central storage of interlanguage links (sometimes known as "interwiki links", although this term also has a different meaning).
Sitelinks between Wiktionary editions are generally not provided through Wikidata, but another function.
Snak is a technical term of Wikibase software which data users are most likely to encounter when accessing Wikidata through the MediaWiki API. It refers to the combination of a property and either a value or one of the special cases "no value" and "unknown value". Snaks can be found in claims (then they are called main snaks) or in qualifiers as part of statements (then they are called qualifier snaks). E.g., in the statement "Emma Watson was a cast member of Harry Potter and the Philosopher's Stone in the role of Hermione Granger" there is a main snak "was a cast member of Harry Potter and the Philosopher's Stone" and a qualifier snak "in the role of Hermione Granger".
A Statement is a piece of data about an item, recorded on the item's page. A statement consists of a claim (a property-value pair such as "Location: Germany", together with optional qualifiers), augmented by references (giving the source for the claim) and a rank (used to distinguish between several claims containing the same property; "normal" by default). Wikidata makes no assumptions about the correctness of statements, but merely collects and reports them with a reference to a source. The term "statement" is often used interchangeably with "claim", but technically it only becomes a statement once at least one reference has been added.
String (also character string) is a general term for a sequence of freely chosen characters interpreted as text like "Hello", as opposed to a value interpreted as a numerical value (like 3.14) or a link to an item (like [[Q1234]]). In addition to a string datatype, Wikidata supports language-specific texts using "monolingual-text" as the value of a property.
Subject, predicate and object are terms sometimes used to describe a claim when viewing entity, property and value as a triple.
Suggestion constraint is a status of a property constraint that provides suggestions of additional improvements. This can be statements with other properties to be added to the item.
Term is a part of entity, includes label, description and alias. Terms may only be plain text (i.e. not containing any wiki markup).
Termbox is the zone at the top of an item page, which includes the labels, the descriptions, and the aliases in different languages.
Title is the name of a page. All pages must have a unique title within a given wiki, as the title is included in the URL for the page. For example, there can be only one page with the title "Douglas Adams" on English Wikipedia. In Wikidata, a title is either an entity identifier such as Q42, or it starts with a namespace prefix such as Help:. The page title is not to be confused with the label for a Wikidata item or property. Wikidata items are connected to pages on other Wikimedia wikis via sitelinks, which use the page's title to uniquely identify the resource.
Triple (or "semantic triple", or "triplet") is the atomic data entity in the RDF data model, which codifies statements in the form of subject–predicate–object expressions.
Unit is a Wikidata item used with a quantity-value. Frequently used units are metre or EUR, but any item could be used as unit. If the unit includes a conversion to SI unit statement, quantities with the unit are normalized based on that. See mw:Wikibase/Indexing/RDF Dump Format#Normalized values.
Value (also datavalue) is the actual piece of information stored within a claim. Wikidata has a range of allowed datatypes, such as "item", "mathematical expression", and "quantity". The datatype needed for any given claim is determined by the property used (e.g. the value in a "place of birth" claim must be an "item"). Instead of a normal value, you can also use one of the special cases "unknown value" or "no value" in a claim.
Value type is the way values are stored internally. Each data type corresponds to one value type. For example, although external identifier, Commons media and mathematical expression are different datatypes, they all use the "string" value type. Values for some data types contain multiple parts with different value types. For example, a quantity contains four parts: "amount", "unit", "upperbound" and "lowerbound", the last two being optional. Unit is a URL which points to a Wikidata item; the other three parts are numbers in string (not floating-point number).
View is a way data can be visualized or accessed. Besides the default view, Wikibase offers views for mobile devices, as well as for rdf and json formats. The data can be accessed with an API. Data on Wikidata is mirrored on Wikidata Query Server offering various result views. Some of the views are editing views, others not. Examples of tools and extensions that provide custom views are Reasonator, Article Placeholder, and Listeria.
Wikibase is the software behind Wikidata. It consists of a set of extensions to the MediaWiki software. These extensions allow Wikidata to manage data in items and properties, and search for this data using queries.
Wikidata is a Wikimedia project that runs an instance of MediaWiki with the Wikibase extensions. It enables Wikidata editors to enter data and browse pages that display it.
Wikidata Query Service (or WDQS) is the official service for querying Wikidata using the SPARQL query language.
Wikimedia is the name of a movement which consists of people and organizations. Wikidata is run by the Wikimedia Foundation together with other wikis such as Wikipedia. The Wikibase software is mainly developed by Wikimedia Germany which is one of the national Wikimedia affiliations.
Wiki is a website that can be edited by the visitors quickly. Wikipedia and Wikidata are wikis.