Editing Web Ontology Language (section)

===Open world assumption===
{{blockquote|[The closed] world assumption implies that everything we don't know is ''false'', while the open world assumption states that everything we don't know is ''undefined''.|Stefano Mazzocchi|''Closed World vs. Open World: the First Semantic Web Battle''<ref>{{cite web |url=http://www.betaversion.org/~stefano/linotype/news/91/ |title=Closed World vs. Open World: the First Semantic Web Battle |first=Stefano |last=Mazzocchi |author-link=Setfano Mazzocchi |date=2005-06-16 |access-date=27 April 2010 |archive-url=https://web.archive.org/web/20090624113015/http://www.betaversion.org/~stefano/linotype/news/91/ |archive-date=24 June 2009 }}</ref>}}

The languages in the OWL family use the [[open world assumption]]. Under the open world assumption, if a statement cannot be proven to be true with current knowledge, we cannot draw the conclusion that the statement is false.

====Contrast to other languages====
A [[relational database]] consists of sets of [[tuple]]s with the same [[Attribute (computing)|attribute]]s. [[SQL]] is a query and management language for relational databases. [[Prolog]] is a [[Logic programming|logical programming]] language. Both use the [[closed world assumption]].