Re: XML Schemas: Best Practices

["Roger L. Costello" <costello@mitre.org>]

Subject: Tutorial on Extending XML Schemas

I have put together a step-by-step tutorial on extending XML Schemas
(with either XSLT/XPath or Schematron).  It contains fully worked
examples, labs (with answers), and batch scripts for running the
examples/labs.  The tutorial may be downloaded from the Best Practice
Homepage:

    http://www.xfront.com/BestPracticeHomepage.html

The tandem of {XSLT/XPath and XML Schemas} or {Schematron and XML
Schemas} is very powerful. I am very excited about this approach. 
Here's a preview of what is covered in the tutorial:

- XML Schemas is very powerful

- However, it is not "all powerful".  There are many constraints 
  that it cannot express.  Here are some examples:

     . Ensure that the value of the aircraft <Elevation> element 
       is greater than the value of the obstacle <Height> element.

     . Ensure that:
          - if the value of the attribute, mode, is "air", then the 
            value of the element, <Transportation>, is either  
            airplane or hot-air balloon,
          - if mode="water" then <Transportation> is either boat 
            or hovercraft,
          - if mode="ground" then <Transportation> is either car 
            or bicycle.

    . Ensure that the value of the <PaymentReceived>  is equal to 
      the value of <PaymentDue>, where these elements are in 
      separate documents!

- To check all our constraints we need to supplement XML 
  Schemas with another tool.  In this tutorial we cover each 
  of these examples and show how the constraints may be implemented 
  using either XSLT/XPath or Schematron.  At the end we examine 
  the pros and cons of each approach.
...

I would like to thank Eddie Robertsson and Rick Jelliffe for helping me
understand the wonderful power of Schematron.  /Roger