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Since the inception of XML, many developers have wondered why we need XML...

How is it better than HTML and what does it do? For starters, XML is far more powerful than HTML, and the power resides in the "X" in XML (which stands for extensible). Rather than providing a set of pre-defined tags (as in the case of HTML), XML specifies the standards with which you can define your own markup languages with their own sets of tags. XML is therefore a meta-markup language, allowing you to define an infinite number of markup languages based upon the standards defined by XML.

XML was created so that richly structured documents could be used over the web. The only viable alternatives, HTML and SGML, are not practical for this purpose. XML allows you to define all sorts of tags with all sorts of rules, such as tags representing business rules or tags representing data description or data relationships.

In this article we're going to take a look at some of the terminology that comes with using XML and its related technologies, as well as how to create and transform XML documents with XSL using Microsoft's MSXML parser. To test the code samples shown in this article you should be running Windows NT/2000/XP with IIS installed. You should also have SQL server 2000 installed on the same machine.

XML Definitions

As with any technology, XML has its own acronym-riddled lingo. Some of the important acronyms include:

XSL: The Extensible Style Language (XSL) is the style language for XML that allows us to transform XML nodes using a set of patterns and templates.

Why XML Should Be Used?

Using XML provides us as developers with a number of benefits. Some of the most obvious benefits include:

XML compresses exceedingly well. Since data compression algorithms operate on the concept of maximizing the entropy of a given input stream, it stands to reason that a highly ordered input stream consisting of regular, repeating tag sequences will compress exceedingly well... much better than standard text which contains generally far less order thus resulting in a decrease in performance.

Weaknesses of XML

XML is obviously not a cure-all language free of any disadvantages... otherwise we would be using XML to markup/represent all of our data, and nothing else! There are of course some drawbacks and weaknesses of XML, namely:

Performance of XML

When you're designing an XML-based Web application, what kind of performance hit do you expect to put on your web server? It's hard to generalize because there are so many variables (such as the size of the XML document, the amount of script code required to process the document, the amount of output generated, etc) to take into consideration, however the following list shows the major variables that can affect the performance of parsing XML:

XML and DOM

Microsoft have provided us with the MSXML parser, which exposes an XML document in the form of a DOM (Document Object Model). With the XML DOM, you can load and parse XML files, gather information about those files, navigate through and manipulate those files. To learn more about the details of the XML DOM, please refer to this site.

Now that we've discussed the reasons for using XML, it's time to look at some source code. We will examine some ASP scripts that create and display XML data. We're going to create an XML file using both static data and data from a database using ADO. The DOM methods createNode and appendChild, as well as the text property are used to construct an in-memory XML tree.

XML with ASP

The following example illustrates how to create an XML tree (in memory) and then persist is to disk using the save method:

<%

%>

In the example above we create an XMLDOM Object. We then create a root node and its child node using the createNode function. Next, we append the nodes after assigning the text property to each of them. Finally, we save the in-memory XML tree to a file, savedI2.xml.

We can also build an XML file from the results of a database query. I've included two files with the support material for this article: pubtest.asp and saved.xsl. Pubtest.asp connects to the SQL Server 2000 pubs database, retrieving several records from the author's table, formatting them as a new XML document and saving that document as saved.xml.

The saved.xsl file contains an XSL style sheet which is used by pubtest.asp to format saved.xml as HTML. You should download the support material before continuing.

Here's an exert from pubtest.asp:

Do While Not rs.EOF
Set onode = xmldoc.createNode("element", "Employee", "")
xmldoc.documentElement.appendChild (onode)
Set inode = xmldoc.createNode("element", "Name", "")
inode.Text = rs.fields(0) & " " & rs.fields(1)
onode.appendChild (inode)

rs.movenext
Loop

One of the XML elements that results from the ASP code shown above looks like this:

<Hi-Tech>
<Employee>
<Name>Bennet Abraham</Name>
<Titles>
<TitleId>BU1032</TitleId>
<royalty>60</royalty>
</Titles>
</Employee>

Here's an extract from the XSL style sheet file, saved.xsl:

<xsl:for-each select="Hi-Tech/Employee">
<TR>
<TD WIDTH="40%" BGCOLOR="lightyellow">
<FONT FACE="Verdana" SIZE="2" COLOR="black">
<xsl:value-of select="Name" />
</FONT>
</TD>
<TD WIDTH="30%" BGCOLOR="lightyellow">
<FONT FACE="Verdana" SIZE="2" COLOR="black">
<xsl:value-of select="Titles/TitleId" />
</FONT>
</TD>
<TD WIDTH="30%" BGCOLOR="lightyellow">
<FONT FACE="Verdana" SIZE="2" COLOR="black">
<xsl:value-of select="Titles/royalty" />
</FONT>
</TD>
</TR>
</xsl:for-each>

When I ran pubtest.asp in my browser, here's what it looked like:

Let's now run through the entire process of retrieving data from the pubs database, saving it to an XML file, and loading and transforming this document as XSL with the MSXML parser.

Our XML example explained

Firstly, we connect to SQL Server 2000 using a system DSN. The DSN is called "pubs", and you should create the DSN using control panel. It should connect to your SQL server, more specifically to its pubs database. We instantiate an ADO connection object, passing in the DSN to its open method:

'Open database connection
Set conn = Server.CreateObject("ADODB.Connection")
dsn = "DSN=pubs;UID=sa;PWD="
conn.Open dsn

Once we're connect to our database, we create a new XML document and assign it a root element called "Hi-Tech". We then proceed to retrieve a recordset from the authors table of our pubs database:

If (xmldoc.childNodes.length = 0) Then
' Build the XML document
Set root = xmldoc.createNode("element", "Hi-Tech", "")
xmldoc.appendChild (root)
' Queries the database for customer data
Sql = "select au_lname,au_fname,au_id from authors"
Set rs = conn.Execute(Sql)
rs.MoveFirst

We then loop through each record in the recordset, appending its title, titleID and royalty fields to the XML document that we created earlier. We use the createNode and appendChild methods to do so:

Set inode = xmldoc.createNode("element", "Titles", "")
onode.appendChild (inode)
Set child = xmldoc.createNode("element", "TitleId", "")
child.Text = rs2.fields(0)
inode.appendChild (child)
Set child = xmldoc.createNode("element", "royalty", "")
child.Text = rs2.fields(1)
inode.appendChild (child)

Once we've retrieved each of the records from the recordset and appended them to our XML document, we save the XML document to our local machine using MSXML's save method:

xmldoc.save server.mappath("saved.xml")

We're now at the point where we have an XML file called saved.xml, as well as the style sheet that's included in the support material for this article, called saved.xml. We instantiate a new XMLDOM object for each of these files, calling the transformNode method of the XML DOM object with a reference to the XML DOM object that contains the XSL file:

sourceFile = Server.MapPath("saved.xml")
styleFile = Server.MapPath("saved.xsl")
set source = Server.CreateObject("Microsoft.XMLDOM")
source.async = false
source.load(sourceFile)
set style = Server.CreateObject("Microsoft.XMLDOM")
style.async = false
style.load(styleFile)

Lastly, we use Response.Write to output the transformed XML to the browser:

Response.Write source.transformNode(style)

Conclusion

Well, I hope this article has answered some of your questions on XML. Hopefully you've learned a thing or two about the advantages and disadvantages of using XML, when it can be used, and most importantly, how it can be used.

Nakul Goyal : A Master of Sciences in Information Technology from Panjab University, Chandigarh and a Bachelor of Computer Applications from Punjab Technical University, Jalandhar, India. He is passionate towards the Cyber World & he likes to write about Technology. He's a Microsoft Certified Professional, a Brainbench Certified 'MVP' (Most Valuable Professional), Brainbench Certified Internet professional and a CIW (Certified Internet Webmaster) Associate. Professionally, Nakul is the co-founder of a Web Designing, Search Engine Optimization Company.

Website: http://www.nakulgoyal.com