Semantics in Wiki - Community-Built Databases: Research and Development - page 248

open nature of the Web. It enables significant flexibility and extensibility in data
modelling. The Semantic Wiki model also allows hybrid modelling with predefined
“schema”, schema-free user-added metadata and unstructured data, thus making the
extension of an application much easier. For example, users can always add new
attributes as needed to a specific article in addition to existing attributes [ 17 ].
According to Bao et al. [ 17 ], some semantic wikis (like SMW) not only preserve
the semantic structure of data, but also provide lightweight query capabilities (with
a role similar to that of SELECT queries in SQL). They gave an example, saying
that in SMW it is possible to pose a query {{ #show [[Category:Article]][[tag::

<

q > Category:food < /q > ]] }} to find all articles tagged with “food” or its subtags

(like “doughnut”).
These authors also argue that because the modelling specification and queries
themselves are also presented as semantic wiki pages, they can be accessed,
updated or deleted in the same fashion as other wiki pages in the browser. There-
fore, semantic wikis function as a virtual abstraction layer over the Web server and
database/file systems so that programmers are not required to directly access the
layers hidden below semantic wikis.
Several MediaWiki extensions provide scripting functionalities. These exten-
sions can be used to support a wide range of lightweight data processing abilities,
including variables, data types and control flow [ 17 ]. In SMW, many elements of a
user interface (UI) in an application can be constructed using scripts. In MediaWiki
(thus, also in SMW), users can also inject JavaScript code into a wiki page by
including either server-side scripts or code in some client-editable special wiki
pages. Some SMW-based applications (e.g. wikicafe.metacafe.com and metavid.
org) have developed advanced UIs such as video browsing and annotation.
Semantic wikis provide a transparent platform for lightweight Web application
development through data modelling, processing and presentation (via a user
interface) abilities. According to Bao et al. [ 17 ], such development model enjoys
several advantages: flexibility, socialisation, inference ability, efficient modelling
ability and safety.
SMW is free software, available as an extension of the popular wiki engine
MediaWiki. Figure 10.5 provides an overview of SMW's core components [ 15 ].
The integration between MediaWiki and SMW is based on MediaWiki's extension
mechanism: SMW registers for certain events or requests, and MediaWiki calls
SMW functions when needed. Hence, SMW does not overwrite any part of Media-
Wiki and can be added to existing wikis without much migration cost.
According to Krotzsch et al. [ 15 ], Semantic MediaWiki (SMW) is a semantically
enhanced wiki engine that enables users to annotate the wiki's contents with
explicit, machine-readable information. By using semantic data, SMW addresses
core problems of today's wikis. MediaWiki is the base software Semantic Media-
Wiki is built on. These authors argue that SMW addresses core problems of today's
wikis including consistency of content, accessing knowledge and reusing knowl-
edge. 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.