XML-Schema (.XSD extension) are documents used to describe the format of XML files. They are similar to DTD (Document type declaration) files but much more powerful.

While working on some XML documents for a Flash site, I stumbled across the XML-Schema editor for Eclipse. The editor shows the XSD as a graphical representation of the model that you’re editing that looks similar to a UML class diagram.

Here’s a great article on how it works.

Benefits of using XSD

As I said, XSD allows you to define the format of your XML document but with much more detail that DTD.

• XSD allows you to type your data (integers, strings, booleans) so that you can better predict what format the xml will be
• It allows the creation of custom types which gives it an object oriented aspect
• You can use all kinds of restrictions for what kind of content can appear within a tag including the number of elements, whether values are required or not, you can even use regular expressions to limit the acceptable values. This is very nice when you’re working with a 3rd party who is generating the XML data.
• Using an XSD file can allow you to automate the validation of an XML file’s format

Once you’ve created your XSD file, you can use the new XML document wizard to create an XML file that links to your schema file. The wizard will automatically populate the XML document with valid data! Furthermore, as you edit the XML file you will get warnings and errors if you go outside the formatting requirements defined in the XSD. For example, if you define a tag <description> as having a maximum length of 128, you will see a visual error if your tag contains more than 128 characters. It’s a great way to forsee problems as you write them.

I hope in the future to write some kind of tool to parse XML based on an XSD file in flash. Apparently, Adobe had created an undocumented Flex feature to validate XML against XSD. Via Misprintt

Installing the XML extensions

Unfortunately, the editor is not installed by default and nstalling software in Eclipse is not very intuitive. I’ve done my best to describe the process here but if you need further help, check this entry.

1. Open Eclipse or FlexBuilder
2. Go to Help>Software Updates… ( > Find and Install for Eclipse 3.3)
   
3. Make sure you have the Europa or Ganymede update sites in the list of update sites:

   Eclipse 3.4 users:
   http://download.eclipse.org/releases/ganymede/
   
   http://download.eclipse.org/releases/europa/site.xml

4. Select the XML and XSD extensions in this screenshot. In Eclipse 3.4 you can search for them, in 3.3 you will have to look through the packages for them manually.
5. Restart Eclipse after the install is complete