Developers Guide to XML

This is the developers guide to XML on theTopXMLwebsite.  On these pages, we package XML in a way that you can easily pick up and use in  Visual Basic, ASP, Cold Fusion and Javascript.

XML - what is it?

XML is a hugely complex topic, you can be a guru on an issue and be completely ignorant of another up and coming area. In this book, we will be restricting our scope of interest to focussing on XML from the perspective of a Visual Basic (or ASP) developer. There is an amazng amount of syntax to learn before you can tutor someone else in XML, but for our needs, we will be focussing on the basics.

XML was born from the shortcomings of SGML [Structured Generalized Markup Language] which was hugely complex, massively flexible and just plain hard to work with for many developers. Needless to say, XML has taken off like a rocket because it has all the best ingredients of SGML without many of the downsides.

So, XML was designed from the ground up to be extensible and to be simple to implement. As a result, it seems that attempt to be simple and to be flexible have resulted in the massive adoption of XML in the computing industry.

Unfortunately anything which is so flexible and extensible will be used for a bewildering array of uses and eventually the number of choices and solutions begin to overlap and perhaps compete with each other.

But not only that, many of the technologies we are going to use, such as XSL and the DOM Level 2, are still subject to change.

As the XSL proposal becomes a recommendation, the object model shipped with IE5 may change and updated objects may be shipped. Should that happen, the methods and properties may change in the new version and the code in this book may need to be changed

However if you are using a combination of IE5 and the MS object such as "Microsoft XML 2.0", then you will be able to use these examples.

Learning more about the XML syntax

If you would like to learn about the details of the syntax of XML, please have a look at our Links section for an appropriate website.

The X(ML) files

Many XML applications have three basic files.

• The .XML file (with the data in it) - which will be indexed and searched by the web search engines (for example)
• Optional file: DTD or Schema file which provides structure for the XML file - this is the vocabulary which your XMl file uses
• Optional file: XSL which provides the "look" of the XML file - this defines how the

Bear in mind that XML files do not need to have DTD or XSL files, as they are optional and serve different purposes to the cre XML file.

How is an XML based application structured?

Overall, this is the pattern which is followed:

How do I create XML files using VB?

For VBScript/ASP developers, use the following syntax to create a new XML document programmatically

<%
Dim xmldoc
Set xmldoc = CreateObject("Microsoft.XMLDOM")
%>

And for VB programmers, you first have to add a reference to your project to the "Microsoft XML, version 2.0" object (you must have installed IE5).  And then you can use:

Dim xmldoc As DOMDocument

Loading a file synchronously

Private sub click_LoadXMLFile()

Dim xmldoc As DOMDocument
Dim docRoot As IDOMNode

‘then load an XML document using the load method as follows:

xmldoc.async = false;
xmldoc.load("http://somewhere.com/test.xml");
Set xmldoc = new DOMDocument
xmldoc.load ("resume.xml")

End Sub

How do I programatically manipulate the XML file?

You saw code above which shows our VB application programmatically loading an XML file.   This was using the DOMDocument object.  To understand what a DOM (document object model) is, first lets look at some HTML code for a table.

<TABLE>
<TBODY>
<TR>
<TD>XML and the Internet for Visual Basic 6 </TD>
<TD>Mark Wilson</TD>
</TR>
<TR>
<TD>Another book </TD>
<TD>Someone Else</TD>
</TR>
</TBODY>
</TABLE>

This would show up in the HTML page as:

From the programmers DOM perspective, you won’t see the table as the user does. Instead you see it as

and using your VB code, you will move around the different node.  It's very sexy!   There are also DOMs for HTML and DHTML, so you can use the same approach to manipulate your HTML files.

For more information, please see our Links page, or our Articles page

For more general information on XML, see our General Guide to XML

For a business summary of XML, see our Business Guide to XML