XPath - Elements and Attributes

Introduction

This is a beginner's tutorial on XSLT and XML. Some knowledge of XML, XSLT, and XPath is required, so read some tutorials if necessary.

Selecting a structure for your data in XML is completely arbitrary. You can represent the same data in several different ways. Below is XML that represents the same data four different ways. The XML represents a Census record. A Census record has a country, a year, a small size, and a large size. This information can be represented by elements or elements and attributes.

• TYPE1 uses attributes and makes a very small footprint.
• TYPE2 uses only elements and because of formatting for readability it uses a little more screen real-estate.
• TYPE3 and TYPE4 use a combination of elements and attributes.

<?xml version="1.0" encoding="utf-8" ?> 
<STUFF>
   <TYPE1>
      <CENSUS COUNTRY="USA" YEAR="1930">
         <PAGE SIZE="SMALL">17x11</PAGE>
         <PAGE SIZE="LARGE">27x19</PAGE>
      </CENSUS>
      
      <CENSUS COUNTRY="USA" YEAR="1880">
         <PAGE SIZE="SMALL">17x11</PAGE>
         <PAGE SIZE="LARGE">19x25</PAGE>
      </CENSUS>
      
      <CENSUS COUNTRY="UK" YEAR="1871">
         <PAGE SIZE="SMALL">9.5x15</PAGE>
         <PAGE SIZE="LARGE">9.5x15</PAGE>
      </CENSUS>
      
      <CENSUS COUNTRY="UK" YEAR="1891">
         <PAGE SIZE="SMALL">11x16</PAGE>
         <PAGE SIZE="LARGE">11x16</PAGE>
      </CENSUS>
   </TYPE1>

   <!-- ***************************************** -->

   <TYPE2>
      <CENSUS>
         <COUNTRY>USA</COUNTRY>
         <YEAR>1930</YEAR>
         <PAGE>
            <SIZE>
               <SMALL>17x11</SMALL>
               <LARGE>27x19</LARGE>
            </SIZE>
         </PAGE>
      </CENSUS>
      
      <CENSUS>
         <COUNTRY>USA</COUNTRY>
         <YEAR>1880</YEAR>
         <PAGE>
            <SIZE>
               <SMALL>17x11</SMALL>
               <LARGE>19x25</LARGE>
            </SIZE>
         </PAGE>
      </CENSUS>
      
      <CENSUS>
         <COUNTRY>UK</COUNTRY>
         <YEAR>1871</YEAR>
         <PAGE>
            <SIZE>
               <SMALL>9.5x15</SMALL>
               <LARGE>9.5x15</LARGE>
            </SIZE>
         </PAGE>
      </CENSUS>
      
      <CENSUS>
         <COUNTRY>UK</COUNTRY>
         <YEAR>1891</YEAR>
         <PAGE>
            <SIZE>
               <SMALL>11x16</SMALL>
               <LARGE>11x16</LARGE>
            </SIZE>
         </PAGE>
      </CENSUS>
   </TYPE2>

   <!-- ***************************************** -->

   <TYPE3>
      <CENSUS>
         <USA YEAR="1930">
            <PAGE SIZE="SMALL">17x11</PAGE>
            <PAGE SIZE="LARGE">27x19</PAGE>
         </USA> 
         
         <USA YEAR="1880">
            <PAGE SIZE="SMALL">17x11</PAGE>
            <PAGE SIZE="LARGE">19x25</PAGE>
         </USA> 
         
         <UK YEAR="1871">
            <PAGE SIZE="SMALL">9.5x15</PAGE>
            <PAGE SIZE="LARGE">9.5x15</PAGE>
         </UK> 
         
         <UK YEAR="1891">
            <PAGE SIZE="SMALL">11x16</PAGE>
            <PAGE SIZE="LARGE">11x16</PAGE>
         </UK> 
      </CENSUS>
   </TYPE3>
   
   <!-- *************************************** -->

   <TYPE4>
      <CENSUS>
         <COUNTRY>
            USA
            <YEAR>
               1930
               <PAGE>
                  <SIZE TYPE="SMALL">17x11</SIZE>
                  <SIZE TYPE="LARGE">27x19</SIZE>
               </PAGE>
            </YEAR>
            <YEAR>
               1880
               <PAGE>
                  <SIZE TYPE="SMALL">17x11</SIZE>
                  <SIZE TYPE="LARGE">19x25</SIZE>
               </PAGE>
            </YEAR>
         </COUNTRY>
         <COUNTRY>
            UK
            <YEAR>
               1871
               <PAGE>
                  <SIZE TYPE="SMALL">9.5x15</SIZE>
                  <SIZE TYPE="LARGE">9.5x15</SIZE>
               </PAGE>
            </YEAR>
            <YEAR>
               1891
               <PAGE>
                  <SIZE TYPE="SMALL">11x16</SIZE>
                  <SIZE TYPE="LARGE">11x16</SIZE>
               </PAGE>
            </YEAR>
         </COUNTRY>

      </CENSUS>
   </TYPE4>
</STUFF>

Points of Interest

Often an XML document needs to be converted to a new structure. That is where XSLT comes in. There are lots of good tutorials on XSLT. I found that there weren''t very many examples that covered more than a few aspects of XSLT. Thus I decided to write an XSLT for each type in my XML document. So, I wrote some XSLT to convert each type into all of the other types. Some things I had to overcome where converting attributes into elements, element values into attributes, selecting nodes back up the tree (the parent in my case), stripping off white space, and adding white space.

The following XSLT converts TYPE2, TYPE3, and TYPE4 into TYPE1.

Notice the following:

• Cycling through each child by using: <xsl:for-each select="PARENTNODE"/>
• Adding attributes to an element: <xsl:attribute name="some_name"><xsl:text>SOME_VALUE</xsl:text></xsl:attribute>
• Adding text as a value: <xsl:text>Your text goes here</xsl:text>
• Adding the value of an element/node: <xsl:value-of select="A/B/C/MY_NODE"/>

  This selects the value of the node MY_NODE that is the child of C that is the child of B that is the child of A.

• Adding comments to the XML for readability: <xsl:comment> YOUR COMMENT HERE </xsl:comment>

<?xml version="1.0" encoding="_TF-8" ?>
<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:template match="/">
  <TYPE1>
   <xsl:for-each select="STUFF/TYPE2/CENSUS">
    <CENSUS>
     <xsl:attribute name="COUNTRY">
      <xsl:value-of select="COUNTRY"/>
     </xsl:attribute>
     <xsl:attribute name="YEAR">
      <xsl:value-of select="YEAR"/>
     </xsl:attribute>
     <PAGE>
      <xsl:attribute name="SIZE">
  <xsl:text>SMALL</xsl:text>
      </xsl:attribute>
      <xsl:value-of select="PAGE/SIZE/SMALL"/>
     </PAGE>
     <PAGE>
      <xsl:attribute name="SIZE">
  <xsl:text>LARGE</xsl:text>
      </xsl:attribute>
      <xsl:value-of select="PAGE/SIZE/LARGE"/>
     </PAGE>
    </CENSUS>
   </xsl:for-each>
   
   <xsl:comment>   -----------------   </xsl:comment>
   <xsl:for-each select="STUFF/TYPE3/CENSUS">
    <xsl:for-each select="child::*">
     <CENSUS>
      <xsl:attribute name="COUNTRY">
  <xsl:value-of select="name()"/>
      </xsl:attribute>
      <xsl:copy-of select="@*"/>
      <xsl:copy-of select="PAGE"/>
     </CENSUS>
    </xsl:for-each>
   </xsl:for-each>
   
   <xsl:comment>   -----------------   </xsl:comment>
   <xsl:for-each select="STUFF/TYPE4/CENSUS">
    <xsl:for-each select="COUNTRY">     
     <xsl:for-each select="YEAR">
      <CENSUS>
  <xsl:attribute name="COUNTRY">
   <xsl:value-of select="normalize-space(../text())"/>
  </xsl:attribute>
  <xsl:attribute name="YEAR">
   <xsl:value-of select="normalize-space(text())"/>
  </xsl:attribute>
  <xsl:copy-of select="PAGE"/>
      </CENSUS>
     </xsl:for-each>
    </xsl:for-each>
   </xsl:for-each>
  </TYPE1>
 </xsl:template>
</xsl:stylesheet>

The following XSLT converts TYPE1, TYPE3, and TYPE4 into TYPE2.

Notice the following:

• Selecting the value of an attribute of a node: <xsl:value-of select="SOMENODE[@SOMEATTRIBUTE='SOMEVALUE']"/>
• Converting a node's name into a node's value: <MYNODE><xsl:value-of select="name()"/></MYNODE>
• Selecting a node's value that has white space around it:

  <xsl:value-of select="normalize-space(text())"/>

  OR selecting the parent node's value that has white space around it:

  <xsl:value-of select="normalize-space(../text())"/>

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:template match="/">
  <TYPE2>
   <xsl:for-each select="STUFF/TYPE1/CENSUS">
    <CENSUS>
     <COUNTRY><xsl:value-of select="@COUNTRY"/></COUNTRY>
     <YEAR><xsl:value-of select="@YEAR"/></YEAR>
     <PAGE>
      <SIZE>
  <SMALL>
   <xsl:value-of select="PAGE[@SIZE='SMALL']"/>
  </SMALL>
  <LARGE>
   <xsl:value-of select="PAGE[@SIZE='LARGE']"/>
  </LARGE>
      </SIZE>
     </PAGE>
    </CENSUS> 
   </xsl:for-each>
   
   <xsl:comment>   -----------------   </xsl:comment>
   
   <xsl:for-each select="STUFF/TYPE3/CENSUS">
    <xsl:for-each select="child::*">
     <CENSUS>
      <COUNTRY><xsl:value-of select="name()"/></COUNTRY>
      <YEAR><xsl:value-of select="@YEAR"/></YEAR>
      <PAGE>
  <SIZE>
   <SMALL>
    <xsl:value-of select="PAGE[@SIZE='SMALL']"/>
   </SMALL>
   <LARGE>
    <xsl:value-of select="PAGE[@SIZE='LARGE']"/>
   </LARGE>
  </SIZE>
      </PAGE>    
     </CENSUS> 
    </xsl:for-each>
   </xsl:for-each>
   
   <xsl:comment>   -----------------   </xsl:comment>
   
   <xsl:for-each select="STUFF/TYPE4/CENSUS">
     <xsl:for-each select="child::COUNTRY">
  <xsl:for-each select="YEAR">
   <CENSUS>
    <COUNTRY><xsl:value-of select="normalize-space(../text())"/>
     </COUNTRY>
    <YEAR>
     <xsl:value-of select="normalize-space(text())"/>
    </YEAR>
    <PAGE>
     <SIZE>
      <SMALL>
       <xsl:value-of select="PAGE/SIZE[@TYPE='SMALL']"/>
      </SMALL>
      <LARGE>
       <xsl:value-of select="PAGE/SIZE[@TYPE='LARGE']"/>
      </LARGE>
     </SIZE>
    </PAGE>
   </CENSUS> 
      </xsl:for-each>
     </xsl:for-each>
   </xsl:for-each>
   
  </TYPE2>
 </xsl:template>
 
</xsl:stylesheet>

The following XSLT converts TYPE1, TYPE2, and TYPE4 into TYPE3.

Notice the following:

• Create an element name from an attribute OR

  convert an attribute into an element or node:

  <xsl:element name="{@ATTRIBUTENAME}">

• To copy an element without change is easy with:

  <xsl:copy-of select="SOMENODE"/>

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:template match="/">
  <TYPE3>
   <CENSUS>
    <xsl:for-each select="STUFF/TYPE1/CENSUS">
     <xsl:element name="{@COUNTRY}">
      <!-- This could be done with <xsl:copy-of select="@YEAR"/> -->
      <xsl:attribute name="YEAR">
  <xsl:value-of select="@YEAR"/>
      </xsl:attribute>
      <xsl:copy-of select="PAGE"/>
     </xsl:element>
    </xsl:for-each>
   </CENSUS>
   
   <xsl:comment>   ---------------   </xsl:comment>
   <CENSUS>
    <xsl:for-each select="STUFF/TYPE2/CENSUS">
     <xsl:element name="{COUNTRY}">
      <xsl:attribute name="YEAR">
  <xsl:value-of select="YEAR"/>
      </xsl:attribute>
      <PAGE>
  <xsl:attribute name="SIZE">
   <xsl:text>SMALL</xsl:text>
  </xsl:attribute>
  <xsl:value-of select="PAGE/SIZE/SMALL"/>
      </PAGE>
      <PAGE>
  <xsl:attribute name="LARGE">
   <xsl:text>SMALL</xsl:text>
  </xsl:attribute>
  <xsl:value-of select="PAGE/SIZE/LARGE"/>
      </PAGE>

     </xsl:element>
    </xsl:for-each>
   </CENSUS>
   
   <xsl:comment>   ---------------   </xsl:comment>
   <CENSUS>
    <xsl:for-each select="STUFF/TYPE4/CENSUS/COUNTRY/YEAR">
     <xsl:element name="{normalize-space(../text())}">
      <xsl:attribute name="YEAR">
  <xsl:value-of select="normalize-space(./text())"/>
      </xsl:attribute>
      <PAGE>
  <xsl:attribute name="SIZE">
   <xsl:text>SMALL</xsl:text>
  </xsl:attribute>
  <xsl:value-of select="PAGE/SIZE[@TYPE='SMALL']"/>
      </PAGE>
      <PAGE>
  <xsl:attribute name="SIZE">
   <xsl:text>LARGE</xsl:text>
  </xsl:attribute>
  <xsl:value-of select="PAGE/SIZE[@TYPE='LARGE']"/>
      </PAGE>
     </xsl:element>
    </xsl:for-each>
   </CENSUS>   
  </TYPE3>
 </xsl:template>
</xsl:stylesheet>   

The following XSLT converts TYPE1, TYPE2, and TYPE3 into TYPE4.

TYPE4 has formatting to make it human readable. Adding formatting to XML is not as easy as I had hoped. It seems advisable to always add formatting by placing it in an xsl:text node.

Notice the following:

• Adding a carriage return: <xsl:text>&#x0D;</xsl:text>
• Adding a line feed: <xsl:text>&#x0A;</xsl:text>
• Adding a tab: <xsl:text>&#x09;</xsl:text>

I only perform the formatting for the conversion of TYPE1 into TYPE4. I found that the formatting statements cluttered the conversion statements.

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<!--
 CARRIAGE RETURN x0D
 LINE FEED x0A
 TAB x09
-->
<xsl:template match="/">
 <CENSUS>
  <xsl:for-each select="STUFF/TYPE1/CENSUS">
   <COUNTRY>
    <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
    <xsl:text>&#x09;</xsl:text> <!-- TAB -->
    <xsl:value-of select="@COUNTRY"/>
    <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
    <xsl:text>&#x09;</xsl:text> <!-- TAB -->
    <YEAR>
     <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
     <xsl:text>&#x09;</xsl:text> <!-- TAB -->
     <xsl:text>&#x09;</xsl:text> <!-- TAB -->
     <xsl:value-of select="@YEAR"/>
     <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
     <xsl:text>&#x09;</xsl:text> <!-- TAB -->
     <xsl:text>&#x09;</xsl:text> <!-- TAB -->
     <PAGE>
      <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
      <SIZE>
  <xsl:attribute name="SMALL">
   <xsl:value-of select="PAGE[@SIZE='SMALL']"/>
  </xsl:attribute>
      </SIZE>
      <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
      <SIZE>
  <xsl:attribute name="LARGE">
   <xsl:value-of select="PAGE[@SIZE='LARGE']"/>
  </xsl:attribute>
      </SIZE>
      <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
      <xsl:text>&#x09;</xsl:text> <!-- TAB -->
     </PAGE>
     <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
     <xsl:text>&#x09;</xsl:text> <!-- TAB -->
    </YEAR>
    <xsl:text>&#x0A;</xsl:text> <!-- LINE FEED -->
   </COUNTRY>
  </xsl:for-each>
 </CENSUS>
 
 <xsl:comment>   ---------------   </xsl:comment>
 <CENSUS>
  <xsl:for-each select="STUFF/TYPE2/CENSUS">
   <COUNTRY>
    <xsl:value-of select="COUNTRY"/>
    <YEAR>
     <xsl:value-of select="YEAR"/>
     <PAGE>
      <SIZE>
  <xsl:attribute name="SMALL">
   <xsl:value-of select="PAGE/SIZE/SMALL"/>
  </xsl:attribute>
      </SIZE>
      <SIZE>
  <xsl:attribute name="LARGE">
   <xsl:value-of select="PAGE/SIZE/LARGE"/>
  </xsl:attribute>
      </SIZE>
     </PAGE>
    </YEAR>
   </COUNTRY>
  </xsl:for-each>
 </CENSUS>
 
 <xsl:comment>   ---------------   </xsl:comment>
 <CENSUS>
  <xsl:for-each select="STUFF/TYPE3/CENSUS/*">
   <COUNTRY>
    <xsl:value-of select="name()"/>
    <YEAR>
     <xsl:value-of select="@YEAR"/>
     <PAGE>
      <SIZE>
  <xsl:attribute name="SMALL">
   <xsl:value-of select="PAGE[@SIZE='SMALL']"/>
  </xsl:attribute>
      </SIZE>
      <SIZE>
  <xsl:attribute name="LARGE">
   <xsl:value-of select="PAGE[@SIZE='LARGE']"/>
  </xsl:attribute>
      </SIZE>
     </PAGE>
    </YEAR>
   </COUNTRY>
  </xsl:for-each>
 </CENSUS>
 
</xsl:template>
</xsl:stylesheet>

  

The C# code necessary to perform the XSL transformations is extremely simple with .NET. Save my XML data with the four types into a file called data.xml. Save the XSLT that you want to run as style.xslt.

static void Main(string[] args)
{
  string fileName = "data.xml";
  FileStream fs = new FileStream(fileName,FileMode.Open,FileAccess.Read);
  XmlTextReader reader = new XmlTextReader(fs);
  s.Seek(0,SeekOrigin.Begin);
  reader = new XmlTextReader(fs);
  TestXSLT(reader,"style.xslt");
}

static void TestXSLT(XmlTextReader reader, string fileName)
{
  System.Console.WriteLine(fileName);

  XslTransform xslt = new XslTransform();
  xslt.Load(fileName);

  XPathDocument xdoc = new XPathDocument(reader);
  XmlTextWriter writer = new XmlTextWriter(Console.Out);
  writer.Formatting=Formatting.Indented;

  xslt.Transform(xdoc, null, writer, null);

}

Conclusion

I hope this has helped you understand XSLT a little better. Study each of the types of Census data in my XML at the top of the document. Look at how they differ. Think of the issues of converting one type to another. Then look at the XSLT that does the conversion.