XML Tutorial/XSLT stylesheet/Boolean Functions

Boolean Functions

boolean() takes an object as its argument and returns a Boolean value. 
    If the argument is a number, true is returned if the number is not zero or NaN. 
    If the argument is a node-set, true is returned if the node-set is not empty. 
    If the argument is a string, true is returned if the string is not empty. 
false() takes no argument and returns the Boolean value false 
lang() takes a string argument. 
       Returns true if the language of the node is the language indicated by the string argument or one of its sublanguages. 
not() takes a Boolean expression as its argument
true() has no argument and returns the Boolean value true

compares "0" as a string and as a number

File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <text>999</text>
    <text>A123</text>
    <text>-16</text>
    <text>0</text>
    <text/>
    <text>false</text>
</data>
File: Transform.xslt
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
      <paragraph>
        <xsl:text>The boolean value of "0" is </xsl:text>
        <B>
          <xsl:value-of select="boolean(//text[text()="0"])"/>
        </B>
        <xsl:text> if "0" is a string, but </xsl:text>
        <B>
          <xsl:value-of select="boolean(number((//text[text()="0"])))"/>
        </B>
        <xsl:text> if "0" is a number.</xsl:text>
      </P>
    </xsl:template>
</xsl:stylesheet>
Output:
<?xml version="1.0" encoding="UTF-8"?><paragraph>The boolean value of "0" is <B>true</B> if "0" is a string, but <B>false</B> if "0" is a number.</P>

Functions true() and false() are useful, when some conditions are tested during programming

File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <number>0</number>
    <number>1</number>
</data>
File: Transform.xslt
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="number">
      <paragraph>
        <xsl:if test="true()">
          <xsl:text>true </xsl:text>
        </xsl:if>
        <xsl:if test="not(false())">
          <xsl:text>not false</xsl:text>
        </xsl:if>
      </P>
    </xsl:template>
</xsl:stylesheet>
Output:
<?xml version="1.0" encoding="UTF-8"?>
    <paragraph>true not false</P>
    <paragraph>true not false</P>

The not function returns true if its argument is false, and false otherwise.

File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <car id="a234" checked="yes"/>
    <car id="a111" checked="yes"/>
    <car id="a005"/>
</data>
File: Transform.xslt
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="car[not(@checked)]">
      <paragraph>
        <B style="color:red">
          <xsl:value-of select="@id"/>
        </B>
      </P>
    </xsl:template>
    <xsl:template match="car[@checked]">
      <paragraph>
        <B style="color:blue">
          <xsl:value-of select="@id"/>
        </B>
      </P>
    </xsl:template>
</xsl:stylesheet>
Output:
<?xml version="1.0" encoding="UTF-8"?>
    <paragraph><B style="color:blue">a234</B></P>
    <paragraph><B style="color:blue">a111</B></P>
    <paragraph><B style="color:red">a005</B></P>

uses node-sets as arguments for boolean() function

File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <text>999</text>
    <text>A123</text>
    <text>-16</text>
    <text>0</text>
    <text/>
    <text>false</text>
</data>
File: Transform.xslt
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
      <TABLE border="1">
        <TR>
          <td>node-set</TH>
          <td>boolean</TH>
        </TR>
        <TR>
          <TD>
            <xsl:text>/</xsl:text>
          </TD>
          <TD>
            <xsl:value-of select="boolean(/)"/>
          </TD>
        </TR>
        <TR>
          <TD>
            <xsl:text>//text</xsl:text>
          </TD>
          <TD>
            <xsl:value-of select="boolean(//text)"/>
          </TD>
        </TR>
        <TR>
          <TD>
            <xsl:text>//number</xsl:text>
          </TD>
          <TD>
            <xsl:value-of select="boolean(//number)"/>
          </TD>
        </TR>
        <TR>
          <TD>
            <xsl:text>//text[23]</xsl:text>
          </TD>
          <TD>
            <xsl:value-of select="boolean(//text[23])"/>
          </TD>
        </TR>
      </TABLE>
    </xsl:template>
</xsl:stylesheet>
Output:
<?xml version="1.0" encoding="UTF-8"?><TABLE border="1"><TR><td>node-set</TH><td>boolean</TH></TR><TR><TD>/</TD><TD>true</TD></TR><TR><TD>//text</TD><TD>true</TD></TR><TR><TD>//number</TD><TD>false</TD></TR><TR><TD>//text[23]</TD><TD>false</TD></TR></TABLE>

Use strings as arguments of boolean() function.

A string is true if and only if its length is non-zero. 

File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <text>999</text>
    <text>A123</text>
    <text>-16</text>
    <text>0</text>
    <text/>
    <text>false</text>
</data>
File: Transform.xslt
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
      <TABLE border="1">
        <TR>
          <td>text</TH>
          <td>boolean</TH>
        </TR>
        <xsl:for-each select="//text">
          <TR>
            <TD>
              <xsl:value-of select="."/>
              <xsl:text/>
            </TD>
            <TD>
              <xsl:value-of select="boolean(text())"/>
            </TD>
          </TR>
        </xsl:for-each>
      </TABLE>
    </xsl:template>
</xsl:stylesheet>
<?xml version="1.0" encoding="UTF-8"?><TABLE border="1"><TR>
<td>text</TH><td>boolean</TH></TR><TR><TD>999</TD><TD>true</TD>
</TR><TR><TD>A123</TD><TD>true</TD></TR><TR><TD>-16</TD><TD>true
</TD></TR><TR><TD>0</TD><TD>true</TD></TR><TR><TD/><TD>false</TD>
</TR><TR><TD>false</TD><TD>true</TD></TR></TABLE>