Help:Introduction to Semantic MediaWiki

Semantic MediaWiki (SMW) is an extension of MediaWiki – the wiki application best known for powering Wikipedia – that helps to search, organise, tag, browse, evaluate, and share the wiki's content. While traditional wikis contain only text which computers can neither understand nor evaluate, SMW adds semantic annotations that allow a wiki to function as a collaborative database. Semantic MediaWiki was first released in 2005, currently has over ten developers, and is in use on hundreds of sites. In addition, a large number of related extensions have been created that extend the ability to edit, display and browse through the data stored by SMW: the term "Semantic MediaWiki" is sometimes used to refer to this entire family of extensions.

Semantic MediaWiki has been funded in part by projects of the Framework Programmes (FP) of the European Union, SEKT and ACTIVE and by project Halo.

Why Semantic Mediawiki?
Wikis have become a great tool for collecting and sharing knowledge in communities. This knowledge is mostly contained within texts and multimedia files, and is thus easily accessible for human readers. But though wikis are very good for storing and retrieving individual facts, they are less useful for getting queried or aggregated information.. As a simple example, consider the following question:


 * «What are the hundred world-largest cities with a female mayor?»

Wikipedia should be able to provide the answer: it contains all large cities, their mayors, and articles about the mayor that tell us about their gender. Yet the question is almost impossible to answer for a human, since one would have to read all articles about all large cities first! Even if the answer is found, it might not remain valid for very long. Computers can deal with large datasets much easier, yet they are not able to support us very much when seeking answers from a wiki: Even sophisticated programs cannot yet read and «understand» human-language texts unless the topic and language of the text is very restricted. The wiki's keyword search does not help either.

Semantic MediaWiki enables wikis to make their knowledge computer-processable, e.g. to answer the above question.

Where SMW can help
Semantic MediaWiki introduces some additional markup into the wiki-text which allows users to add "semantic annotations" to the wiki. While this first appears to make things more complex, it can also greatly simplify the structure of the wiki, help users to find more information in less time, and improve the overall quality and consistency of the wiki. Here are some of the benefits of using SMW:


 * Automatically-generated lists. Wikis tend to contain many aggregated lists; Wikipedia itself has thousands, like "List of metropolitan areas in Spain by population". Those lists are prone to errors, since they have to be updated manually. Furthermore, the number of potentially interesting lists is huge, and it is impossible to provide all of them in acceptable quality. In SMW, lists are generated automatically like this. They are always up-to-date and can easily be customised to obtain further information.


 * Visual display of information. The various display formats defined by additional extensions, such as Semantic Result Formats and Semantic Maps, allow for displaying of information in calendars, timelines, graphs and maps, among others, providing a much richer view of the data than simple lists would.


 * Improved data structure. MediaWiki wikis tend to make heavy use of categories for structuring data. While these are generally helpful, consider the categories on Wikipedia called "Rivers in Buckinghamshire" and "1620s deaths"; if the information in these pages were stored using SMW, these categories could be replaced by simple queries, reducing the need for a complex classification system. In addition, if semantic markup within the wiki is stored within templates, otherwise known as semantic templates, a wiki can easily gain a solid data structure. And the Semantic Forms extension lets administrators create forms for adding and editing the data within semantic templates, thus making the addition of semantic information possibly even easier and more straightforward than regular wiki text.


 * Searching information. Individual users can search for specific information by creating their own queries, supported via extensions like Halo and Semantic Drilldown.


 * Inter-language consistency. In wikis that span multiple languages, like Wikipedia, there is often a great deal of data redundancy, which can lead to inconsistencies. For example, the population of Edinburgh at the time of this writing is different in the English, German, and French Wikipedias. If data is stored semantically, you could, for instance, ask for the population of Beijing that is given in the Chinese Wikipedia without knowing a single word of that language. This can be exploited to have different languages query one another's data, either for reuse or at least to detect inconsistencies.


 * External reuse. Data, once it is created in an SMW wiki, does not have to remain within the wiki; it can easily be exported via formats like CSV, JSON and RDF. This enables an SMW wiki to serve as a data source for other applications, or, in the case of enterprise usages, to take over the role that a relational database would normally play. Through the use of the External Data extension and the result format Exhibit, one SMW-based wiki can even use the data from another, eliminating the need for redundancy between wikis. You can also query SMW's data via an RDF triplestore, using any of the available triplestore connector extensions.


 * Integrate and mash-up data. Data contained in an SMW installation does not have to be an isolated store of information. Extensions such as the Data Import, Data Transfer and External Data extensions empower you to integrate external data (coming e.g. from legacy systems, web services or linked data sources) and interrelate it with existing semantic data in the wiki. Thus, an SMW-powered wiki can serve as a central information hub in an IT landscape.

Who is using Semantic MediaWiki?
Semantic MediaWiki has grown a long way from its roots as an academic research project. It is currently in active use in hundreds of sites, in many languages, around the world, including Fortune 500 companies, biomedical projects, government agencies and consumer directories. The Wikipedia article on Semantic MediaWiki contains a section listing some of its notable usages. You can also see one list of the sites that use SMW here, and another here. It should be noted that both lists focus on public sites, although perhaps half or more of the sites that use Semantic MediaWiki are private, for internal use by companies and organizations.

There are a number of consulting companies that implement SMW as part of their solutions, including Benchmarking Partners, FZI, LeveragePoint, ontoprise and WikiWorks. (You can see a listing of people and companies that can be hired to do SMW-based work at the "work for hire" page.)

At least two websites currently offer hosting of Semantic MediaWiki and some of its extensions: Wikia and Referata.

You can read about positive experiences using SMW among companies, organizations and individuals at the testimonials page.

More information
The SMW site has much more information about setting up and running a Semantic MediaWiki installation. The administrator manual holds information on downloading, installing and troubleshooting SMW; and also has information on the various extensions that can be installed to work together with SMW. The user manual holds information on defining properties, running queries, browsing data and the like. And the FAQ has answers to frequently-asked questions on both technical and non-technical issues.

Contact and user support
For contacting the SMW Project, see the contact page. For comments and questions, there is an active user mailing list that you can join, as well as an IRC Channel, #semantic-mediawiki. See Help:Getting support for further information about support for SMW.

Bugs and feature requests for SMW can also be filed at MediaZilla; see the documentation on reporting bugs.