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The [[Help:Properties and types|datatype]] '''Boolean''' is for attributes that can only have two possible values. You can enter "true" or "false", also 1/0, yes/no, t/f, and y/n. Other languages may provide language-specific options.

To allow two arbitrary strings, or more than two possible values (such as <tt>no</tt> - <tt>maybe</tt> - <tt>probably</tt> - <tt>yes</tt>) use [[Type:String]] with [[Property:Allows value]] to restrict the possible values. In many circumstances it may also be more appropriate to use a category instead of a Boolean.

== Displaying Boolean values in inline queries ==

By default, Boolean values will display <tt>true</tt> and <tt>false</tt> in [[Help:semantic search|queries]]. This can be changed by specifying a format string to control what is displayed for the true and false values of a property. Consider, e.g., a Boolean property <tt>successful</tt> in a wiki about projects, that describes whether or not a certain project was a success. Displaying all projects with their success status could then be achieved as follows:

<pre><nowiki>{{#ask: [[Category:Project]]
 ?successful#success,failure
}}</nowiki></pre>

where <tt>success</tt> and <tt>failure</tt> are displayed in a result column labelled "successful". Note that this column may have empty fields, for projects where the success or failure was not determined yet. This is a difference to categories, which can either be true or unset, but not explicitly set to false. So if we would have used a category <tt>Category:Successful project</tt> then we could have created only the following query:

<pre><nowiki>{{#ask: [[Category:Project]]
 ?Category:Successful project#success,failure
}}</nowiki></pre>

I this case, an extra cloumn labelled "Sucessful" appears again, but now showing <tt>success</tt> for all results that belong to the category <tt>Successful</tt>, and showing <tt>failure</tt> for all other cases (including those where the status may be unknown).

In both of the above cases, it is possible to use "=" to change the label of the rsul column, as usual, e.g.:

<pre><nowiki>{{#ask: [[Category:Project]]
 ?successful#success,failure=Success status
}}</nowiki></pre>

A special formatting symbol for Booleans is the lower-case letter <tt>x</tt>. When given as a text for displaying results, SMW will use an <tt>X</tt> that resembles a cross for true.

<pre><nowiki>{{#ask: [[Category:Project]]
 ?successful#x
}}</nowiki></pre>

This would show a cross for all cases where the property is set to true, and nothing if it is false or unset. Finally, the labels given for true and false (or category membership and non-membership) can also be special symbols or images, and may also be empty to show nothing (however, in at least the comma should always be set). So to display a tick (actually a square root symbol) for true one could use:

<pre><nowiki>{{#ask: [[Category:Project]]
 ?successful#&#x221a;,
}}</nowiki></pre>

{{docu|master page=Type:Boolean|language=en|minversion=1.0}}