1. Why XML Value Validation

2. XML Schema Validation

In the 'old' days of comma delimited file exchanges, it was up to the receiving application to determine whether incoming data is complete, valid and fit for processing. XML provides opportunities for improvements:

• XML Schema Validation

• XML Value Validation

Using W3C XML Schema, messages can be structurally validated by sender and/or receiver, regardless of their platforms. The XML Schema validation includes checking for:

• Correct XML tag names

• Correct nesting structure

• Presence of mandatory element and attributes

• Correct number of maximum tag occurrences

• Data type conformance

Such W3C XML Schema Structure Validation is a major improvement. Application design can be simplified, because the message can be structurally validated, and if necessary rejected, before it reaches the application.

For a message to be truly valid, i.e. complying in full with the data exchange partner agreement, the structural validation does not suffice: The values embedded in the message need to be validated too. Such Value Validation has commonly been encoded within custom built applications. There is the risk that the Value Validation is not equivalent when the data exchange partners use different applications. They may even produce inconsistent error messages for one and the same XML instance.

The effort required to build the validation logic in each application and the issues associated with such decentralised, platform-dependent value validation call for an improvement: Wouldn't it be great if the values within an XML instance could be validated just the way we validate its structure against the XML Schema, using platform-independent open standards?

There is good news: In 2006 OASIS defined UMCLVV, the draft OASIS UBL Methodology for Code List and Value Validation. While UMCLVV was designed to meet UBL needs, it could be applied to any context. UMCLVV has since been split into three fully approved standards: OASIS Genericode 1.0, OASIS Context Value Association 1.0 and ISO Schematron. The deployment of these integrated standards delivers some major benefits:

• A standardised XML format for code lists: OASIS Genericode. For details, see Tony Coates and UBL Code List Representation Technical Committee

• Adoption and re-use of Genericode lists defined by external bodies (ISO, UN/CEFACT, Statistics New Zealand, etc.)

• Restrictions and extensions of standardised code lists

• Context-specific code list validation using OASIS Context Value Association

• Meta data validation for code lists

• Complex business rule validation using ISO Schematron

• Platform-independent validation

• Simple run-time requirement: XSLT W3C Stylesheet Transformation

• Consistent error messages, default or user-defined

• Using open standards: XML, OASIS Genericode 1.0, OASIS Context Value Association 1.0, W3C XPath, ISO Schematron, XSLT

• One validation standard applicable to any XML context

• Opportunities to gradually improve data quality, using fatal errors and optionally warnings

• Opportunities to simplify application design and testing

XML Value Validation has been successfully implemented at the New Zealand Ministry of Education since 2006.

XML Value Validation can be deployed in isolation of the Model-driven XML Vocabulary (MXV) methodology and tools. However, when used in conjunction with MXV, all skeleton input files for the XML Value Validation are generated by MXV, saving time and avoiding errors.

Data Management Solutions can

• offer hands-on consulting expertise for XML Value Validation,

• provide training when introducing XML Value Validation,

• develop and deliver XML Value Validation artefacts for your organisation's validation requirements,

• implement XML Value Validation at your organisation, with or without MXV

For any XML Value Validation related enquiries, please contact me.

August 2011:

Added support for W3C Stylesheet Version 2 (XSLT2), allowing more complex, XSLT2 based value validations in Schematron asserts.

For example, date calculations are now much easier to achieve, particularly when relative to the current date.

For details on what is new in XSLT2, see http://www.w3.org/TR/xslt20/#whats-new-in-xslt2

October 2010

Added support for OASIS Genericode 1.0 and OASIS Context Value Association 1.0 Committee Specifications

MXV has now improved support for generating new versions of XML Value Validation files whilst retaining the business content of the preceding version:

• OASIS Genericode files (retains values and codes)

• OASIS Context Value Association files (retains lists and contexts)

• ISO Schematron Business Constraints files (retains patterns and rules)

MXV utilises the following copyrighted artefacts:

• OASIS copyrights:

  • OASIS Genericode 1.0 Committee Specification: http://docs.oasis-open.org/codelist/cs-genericode-1.0/doc/oasis-code-list-representation-genericode.pdf

  • OASIS Context Value Association 1.0 Committee Specification: http://docs.oasis-open.org/codelist/cs01-ContextValueAssociation-1.0/doc/context-value-association.pdf

   

• Crane Softwrights copyrights:

  • Crane Softwrights Genericode and CVA file rendering stylesheets: http://cranesoftwrights.com/resources/ubl/index.htm#codess

  • Crane Softwrights Schematron implementation of CVA files for validation: http://cranesoftwrights.com/resources/ubl/index.htm#cva2sch