A semantic wiki is a

wiki A wiki ( ) is an online hypertext publication collaboratively edited and managed by its own audience, using a web browser. A typical wiki contains multiple pages for the subjects or scope of the project, and could be either open to the pub ...

that has an underlying model of the knowledge described in its pages. Regular, or

syntactic In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure (constituency) ...

, wikis have structured text and untyped

hyperlink In computing, a hyperlink, or simply a link, is a digital reference to data that the user can follow or be guided by clicking or tapping. A hyperlink points to a whole document or to a specific element within a document. Hypertext is text w ...

s. Semantic wikis, on the other hand, provide the ability to capture or identify information about the data within pages, and the relationships between pages, in ways that can be queried or exported like a

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

through semantic queries. Semantic wikis were first proposed in the early 2000s, and began to be implemented seriously around 2005. As of 2021, well-known semantic wiki engines are

Semantic MediaWiki Semantic MediaWiki (SMW) is an extension to MediaWiki that allows for annotating semantic data within wiki pages, thus turning a wiki that incorporates the extension into a semantic wiki. Data that has been encoded can be used in semantic search ...

and Wikibase.

Key characteristics

Formal notation

The knowledge model found in a semantic wiki is typically available in a

formal language In logic, mathematics, computer science, and linguistics, a formal language consists of words whose letters are taken from an alphabet and are well-formed according to a specific set of rules. The alphabet of a formal language consists of sym ...

, so that machines can process it into an entity-relationship model or

relational database A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relati ...

. The formal notation may be included in the pages themselves by users, as in

, or it may be derived from the pages or the page names or the means of linking. For example, using a specific alternative page name might indicate that a specific type of link was intended. Providing information through a formal notation allows machines to calculate new facts (e.g. relations between pages) from the facts represented in the knowledge model.

Semantic Web compatibility

The technologies developed by the Semantic Web community provide one basis for formal reasoning about the knowledge model that is developed by importing this data. However, there is also a wide array of technologies that work on relational data.

Example

Imagine a semantic wiki devoted to

food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...

. The page for an

apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...

would contain, in addition to standard text information, some machine-readable or at least machine-intuitable semantic data. The most basic kind of data would be that an apple is a kind of

fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in partic ...

—what's known as an

inheritance Inheritance is the practice of receiving private property, titles, debts, entitlements, privileges, rights, and obligations upon the death of an individual. The rules of inheritance differ among societies and have changed over time. Of ...

relationship. The wiki would thus be able to automatically generate a list of fruits, simply by listing all pages that are tagged as being of type "fruit." Further semantic tags in the "apple" page could indicate other data about apples, including their possible colors and sizes, nutritional information and serving suggestions, and so on. If the wiki exports all this data in RDF or a similar format, it can then be queried in a similar way to a database—so that an external user or site could, for instance, request a list of all fruits that are red and can also be baked in a pie.

History

In the 1980s, before the Web began, there were several technologies to process typed links between collectively maintained hypertext pages, such as NoteCards, KMS, and gIBIS. Extensive research was published on these tools by the

collaboration software Collaborative software or groupware is application software designed to help people working on a common task to attain their goals. One of the earliest definitions of groupware is "intentional group processes plus software to support them". As re ...

computer-mediated communication Computer-mediated communication (CMC) is defined as any human communication that occurs through the use of two or more electronic devices. While the term has traditionally referred to those communications that occur via computer-mediated forma ...

hypertext Hypertext is text displayed on a computer display or other electronic devices with references ( hyperlinks) to other text that the reader can immediately access. Hypertext documents are interconnected by hyperlinks, which are typically ...

, and

computer supported cooperative work Computer-supported cooperative work (CSCW) is the study of how people utilize technology collaboratively, often towards a shared goal. CSCW addresses how computer systems can support collaborative activity and coordination. More specifically, the ...

communities. The first known usage of the term "Semantic Wiki" was a

Usenet Usenet () is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived the idea in 1979, and it wa ...

posting by Andy Dingley in January 2001. Its first known appearance in a technical paper was in a 2003 paper by Austrian researcher Leo Sauermann. Many of the existing semantic wiki applications were started in the mid-2000s, including ArtificialMemory (2004), Semantic MediaWiki (2005), Freebase (2005), and

OntoWiki OntoWiki is a free and open-source semantic wiki application, meant to serve as an ontology editor and a knowledge acquisition system. It is a web-based application written in PHP and using either a MySQL database or a Virtuoso triple store. Ont ...

(2006). June 2006 saw the first meeting dedicated to semantic wikis, the "SemWiki" workshop, co-located with the

European Semantic Web Conference The Extended Semantic Web Conference (abbreviated as ESWC), formerly known as the European Semantic Web Conference, is a yearly international academic conference on the topic of the Semantic Web. The event began in 2004 as the European Semantic W ...

Montenegro ) , image_map = Europe-Montenegro.svg , map_caption = , image_map2 = , capital = Podgorica , coordinates = , largest_city = capital , official_languages = ...

. This workshop ran annually until 2010. The site

DBpedia DBpedia (from "DB" for " database") is a project aiming to extract structured content from the information created in the Wikipedia project. This structured information is made available on the World Wide Web. DBpedia allows users to semanti ...

, launched in 2007, though not a semantic wiki, publishes structured data from

Wikipedia Wikipedia is a multilingual free online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and using a wiki-based editing system. Wikipedia is the largest and most-read refer ...

in RDF form, which enables semantic querying of Wikipedia's data. In March 2008,

Wikia Fandom (formerly known as Wikicities before 2007 and later Wikia before 2019) is a wiki hosting service that hosts wikis mainly on entertainment topics (i.e. video games, TV series, movies, entertainers, etc.). Its domain is operated by Fandom, ...

, the world's largest wiki farm, made the use of Semantic MediaWiki available for all their wikis on request, thus allowing all the wikis they hosted to function as semantic wikis. However, since upgrading to version 1.19 of MediaWiki in 2013, they have stopped supporting Semantic MediaWiki for new requests on the basis of performance problem. In July 2010,

Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...

purchased Metaweb, the company behind Freebase. In April 2012, work began on

Wikidata Wikidata is a collaboratively edited multilingual knowledge graph hosted by the Wikimedia Foundation. It is a common source of open data that Wikimedia projects such as Wikipedia, and anyone else, can use under the CC0 public domain license ...

, a collaborative, multi-language store of data, whose data could then be used within Wikipedia articles, as well as by the outside world.

Semantic wiki software

There are a number of wiki applications that provide semantic functionality. Some standalone semantic wiki applications exist, including

. Other semantic wiki software is structured as extensions or plugins to standard wiki software. The best-known of these is

, an extension to

MediaWiki MediaWiki is a free and open-source wiki software. It is used on Wikipedia and almost all other Wikimedia websites, including Wiktionary, Wikimedia Commons and Wikidata; these sites define a large part of the requirement set for Media ...

. Another example is the SemanticXWikiSemantic XWikiExtension
ObjectSecurity Ltd, November 16, 2012 extension for

XWiki XWiki is a free wiki software platform written in Java with a design emphasis on extensibility. XWiki is an enterprise wiki. It includes WYSIWYG editing, OpenDocument based document import/export, semantic annotations and tagging, and advanced per ...

. Some standard wiki engines also include the ability to add typed, semantic links to pages, including

PhpWiki PhpWiki is a web-based wiki software application. It began as a clone of WikiWikiWeb and was the first wiki written in PHP. PhpWiki has been used to edit and format paper books for publication. History The first version, by Steve Wainstead, was re ...

and

Tiki Wiki CMS Groupware Tiki Wiki CMS Groupware or simply Tiki, originally known as TikiWiki, is a free and open source Wiki-based content management system and online office suite written primarily in PHP and distributed under the GNU Lesser General Public License (LG ...

. Freebase, though not billed as a wiki engine, is a web database with semantic-wiki-like properties.

Common features

Semantic wikis vary in their degree of formalization. Semantics may be either included in, or placed separately from, the wiki markup. Users may be supported when adding this content, using forms or

autocompletion Autocomplete, or word completion, is a feature in which an application predicts the rest of a word a user is typing. In Android and iOS smartphones, this is called predictive text. In graphical user interfaces, users can typically press the t ...

, or more complex proposal generation or consistency checks. The representation language may be wiki syntax, a standard language like RDF or

OWL Owls are birds from the order Strigiformes (), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers a ...

, or some database directly populated by the tool that withdraws the semantics from the raw data. Separate versioning support or correction editing for the formalized content may also be provided. Provenance support for the formalized content, that is, tagging the author of the data separately from the data itself, varies. What data can get formalized also varies. One may be able to specify types for pages, categories, or paragraphs or sentences (the latter features were more common in pre-web systems). Links are usually also typed. The source, property, and target may be determined by some defaults, e.g. in Semantic MediaWiki the source is always the current page. Reflexivity also varies. More reflexive user interfaces provide strong ontology support from within the wiki, and allow it to be loaded, saved, created, and changed. Some wikis inherit their ontology entirely from a pre-existing strong ontology like Cyc or

SKOS Simple Knowledge Organization System (SKOS) is a W3C recommendation designed for representation of thesauri, classification schemes, taxonomies, subject-heading systems, or any other type of structured controlled vocabulary. SKOS is part of th ...

, while, on the other extreme, in other semantic wikis the entire ontology is generated by users. Conventional, non-semantic wikis typically still have ways for users to express data and metadata, typically by tagging, categorizing, and using

namespace In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified. Namespaces ...

s. In semantic wikis, these features still typically exist, but integrated these with other semantic declarations, and sometimes with their use restricted. Some semantic wikis provide

reasoning Reason is the capacity of consciously applying logic by drawing conclusions from new or existing information, with the aim of seeking the truth. It is closely associated with such characteristically human activities as philosophy, science, langu ...

support, using a variety of engines. Such reasoning may require that all instance data comply with the ontologies. Most semantic wikis have simple querying support (such as searching for all triples with a certain subject, predicate, object), but the degree of advanced query support varies; some semantic wikis provide querying in standard languages like

SPARQL SPARQL (pronounced " sparkle" , a recursive acronym for SPARQL Protocol and RDF Query Language) is an RDF query language—that is, a semantic query language for databases—able to retrieve and manipulate data stored in Resource Description ...

, while others instead provide a custom language. User interface support to construct these also varies. Visualization of the links especially may be supported. Many semantic wikis can display the relationships between pages, or other data such as dates, geographical coordinates, and number values, in various formats, such as graphs, tables, charts, calendars, and maps.

References

External links

Semantic wiki
article a
SemanticWeb.org

Semantic wiki projects
- contains a list of active, defunct and proposed semantic wiki applications
SemanticWiki mini-series
- a mini-series of online conferences about semantic wikis that ran in 2008 and 2009. {{Semantic Web Semantic wiki software Wikis by genre