XML Reference Guide

Mar 14, 2003

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In a previous guide entry, I've told you about some of the various versions of RSS, an XML format used for syndicating content. Today I'm going to talk about transforming an XML document created by SQL Server into RSS using Visual Basic .NET.

Let's start by looking at the source. Assume, for example, that we have a database table that looks like this:

CREATE TABLE RSSFeed 
	(
	ItemID int identity (1, 1) NOT NULL 
	, ItemName varchar (100) NULL
	, PublishDate smalldatetime NULL
	, ItemDesc varchar (500) NULL
	, ItemURL varchar(100) NULL
	)

If we were to do a query on SQL Server, we might (depending on the options we choose) get a document something like this:

<ROOT>
   <RSSFeed ItemID="c388ad07-8f55-438b-a587-a19b75a052ba"
      ItemName="Blog :: New Sun Web Services Developer Title Now Live"
      PublishDate="July 30, 2004" 
      ItemDesc="So you can build web services applications. Prove it. Now you can, with..."
      ItemURL="http://www.informit.com/discussion/index.asp?postid=c388ad07-8f55-438b-a587-a19b75a052ba" />

   <RSSFeed ItemID="3c08e7f7-49d3-4487-8fe5-82953c633e6c"
      ItemName="Blog :: What's so great about Grid?"
      PublishDate="July 28, 2004" 
      ItemDesc="I'm glad to see that grid computing is starting to pop up more frequently. In fact, ..."
      ItemURL="http://www.informit.com/discussion/index.asp?postid=3c08e7f7-49d3-4487-8fe5-82953c633e6c" />
</ROOT>

We could, if we so desired, use XSL Transformations to turn this into any number of RSS formats. (In fact, we could do all nine, if we were that ambitious.) For example, we could turn this format into a simple RSS .91 feed with this stylesheet:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
   version="1.0">
<xsl:output method="html"/>

<xsl:template match="/">

<rss version="2.0">
  <channel>
    <title>InformIT :: XML Reference Guide</title>
    <link>http://www.informit.com/</link>
    <description>The latest weblog and content updates for 
the InformIT-XML Reference Guide</description>

    <language>en</language>
    <xsl:apply-templates />
  </channel>
</rss>

</xsl:template>

<xsl:template match="RSSFeed">
  <item>
    <title><xsl:value-of select="@ItemName" /></title>
    <link><xsl:value-of select="@ItemURL" /></link>
    <description><xsl:value-of select="@ItemDesc" /></description>

  </item>
</xsl:template>

</xsl:stylesheet>

But how do we actually perform the transformation in .NET? It turns out to be remarkably straightforward.

If you're already familiar with creating .NET applications, skip ahead to the next paragraph. For those of you who are not, stay with me here:

Create a text file called TranslateRSS.vb. (We'll populate it in a moment.)

Create a script file called buildTrans.bat and add the following text:

vbc.exe /t:exe /debug+ /optionstrict+ /out:.\TranslateRSS.exe TranslateRSS.vb /r:System.dll,System.Xml.dll

Save buildTrans.bat in the same directory as TranslateRSS.vb.
When you're ready, run buildTrans.bat to build the VB.NET file into an application, TranslateRSS.exe.
Run TranslateRSS.exe to see the results.

OK, now that we've taken care of the mechanics, let's look at the application itself. The framework is easy:

Option strict off

Imports Microsoft.VisualBasic
Imports System
Imports System.IO

public class TransformXMLSample

    shared sub Main()

       Console.WriteLine ("Transformation will go here.")

    end sub

end Class

Now we can add the actual transformation:

Option strict off

Imports Microsoft.VisualBasic
Imports System
Imports System.IO

Imports System.Xml
Imports System.Xml.Xsl

public class TransformXMLSample

    shared sub Main()

       Dim xslt As New XslTransform()
       Dim resolver as XmlUrlResolver = new XmlUrlResolver()

       xslt.Load(CType("rss.xsl", String))

       xslt.Transform("rssdata.xml", "rssout.xml", resolver)

    end sub

end Class

Note that I'm assuming that the database information has been written to a file. You could just as easily output it to a stream and use the stream as the input for the transformation.

The result is an RSS 2.0 file:

<rss version="2.0">

  <channel>
    <title>InformIT :: XML Reference Guide</title>
    <link>http://www.informit.com/
    <description>The latest weblog and content updates for the InformIT-XML Reference Guide</description>
    <language>en</language>

    <item>
      <title>Blog :: New Sun Web Services Developer Title Now Live</title>
      <link>http://www.informit.com/discussion/index.asp?postid=c388ad07-8f55-438b-a587-a19b75a052ba
      <description>So you can build web services applications. Prove it. Now you can, with...</description>
    </item>

    <item>
      <title>Blog :: What's so great about Grid?</title>
      <link>http://www.informit.com/discussion/index.asp?postid=3c08e7f7-49d3-4487-8fe5-82953c633e6c
      <description>I'm glad to see that grid computing is starting to pop up more frequently. In fact, ...</description>
    </item>

  </channel>
</rss>

The beauty of this approach is that you can actually provide your readers with a variety of choices by simply adding subsequent transofmraitons that transform the data into a variety of formats, including Atom, leaving all of them for readers to choose or toss aside.

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