[New-ITS] Java validation (was: RE: Schemas for Validation??)

[Grahame Grieve]

interesting points.

What makes the difference is the availability of extra
schematic information in various files that would be brought
be bear - MIF, XMI, abstract constraints, etc

the other important thing is the use of the extensions
to provide terminology.

Grahame

ann.wrightson at bt.com wrote:
> Here is a response from Inigo Surguy (inigo.surguy at csw.co.uk):
> 
> Compared to W3C XML Schema, I agree that many approaches can provide
> better validation, and if that was the only option, then I would agree
> that Java validation would be a reasonable choice.
> 
> However, I think it makes more sense to use Schematron as a validation
> language rather than Java. The pros of the Java validation approach are
> all pros of Schematron, too (except probably the speed), and Schematron
> is easier to write, and more generally supported.
> 
> With the Java approach, you still need some way of specifying the
> constraints that will be applied to the document, and the most obvious
> choice is to use XPath. Then, it makes sense for the XPaths to be held
> in a properties file so they can be changed without recompilation, and
> it makes sense to associate an error message with each XPath as well. Go
> any distance down this route and you end up reinventing Schematron!
> 
> The only significant reason I can see for using Java over Schematron is
> for memory and performance efficiency. Constraints can be checked using
> a streaming Java SAX implementation without having to read the entire
> HL7 document into memory, which allows very large documents to be
> handled without problems. Empirically, I found during PSIS development
> that reading HL7 via SAX and validating it with some simple constraints
> written in Java was about twice as fast as doing the same via Java using
> XPath. A Schematron implementation would be slower again than
> Java+XPath. However, I don't consider the performance benefit a viable
> reason for choosing Java over another validator.
> 
> When I was working on PSIS, I did write a simple Java HL7 validator.
> However, this worked by applying a W3C Schema, and a Schematron schema.
> The Java code made it easy to apply it to multiple messages
> simultaneously, and the Schematron made it easy to write the validation
> code. The Schematron code was using XSLT 2 Schematron (and hence had
> regex support, etc.) with some XSLT 2 functions to abstract common
> checks. This worked well, and non-Java programmers were able to extend
> it and improve it.
> 
> This is the approach I recommend - using Schematron to write the
> validation rules, and Java (.NET, whatever) to apply the validation. I
> think this suits the strengths of both languages. In addition - for
> those constraints which are difficult to express in Schematron, then you
> can use Java extension functions from within the XSLT Schematron
> implementation. As long as the definition of these extensions is clear,
> then they could equally well be implemented in .NET, or pure XSLT, or
> any other language - see the EXSLT project for an example of this
> approach.
> 
> Cheers
> 
> Inigo
> 
>  
> 

-- 
Grahame Grieve
CTO, Jiva Medical       Software Integration Tools
CTO, Kestral Computing  Healthcare Applications