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How to Specify Validation Information

Roger L. Costello27 December, 2008

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Validation Information

<?xml version="1.0"?><Library xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation= "http://www.book.org Book.xsd http://www.employee.org Employee.xsd"> <Books> … </Books> <Employees> … </Employees></Library>

Validate the items in the http://www.book.org namespace against Book.xsd, and the items in the http://www.employee.org namespace against Employee.xsd.

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Embedded Validation Information

<?xml version="1.0"?><Library xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation= "http://www.book.org Book.xsd http://www.employee.org Employee.xsd"> <Books> … </Books> <Employees> … </Employees></Library>

The validation information is embedded within the XML instance document

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It's not always a good idea to embed validation information in

XML instance documents

Reason #1

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Document Lifecycle

• Some XML instance documents are validated against different schemas at different stages of the document’s lifecycle, particularly in workflow-based applications.

Rob Sally Pete Jill Anthony

Schema1 Schema2 Schema3 Schema4

XML

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Rob Sally Pete Jill Anthony

Schema1 Schema2 Schema3 Schema4

The validation information inside the XML instance document will have to be changed at every stage in the workflow.

XML

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It's not always a good idea to embed validation information in

XML instance documents

Reason #2

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Diverse Schema Languages

<?xml version="1.0"?><Library xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation= "http://www.book.org Book.xsd http://www.employee.org Employee.xsd"> <Books> … </Books> <Employees> … </Employees></Library>

This validation information is limited to only XSD schemas

• The XML instance document may be composed of XML vocabularies from different schema languages.

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Popular Tag SetsDTD

XHTML

Relax NG

SVG

XML Dig-Sig

XML Schema

GML

Docbook

Atom

IMS Question & Test

DITA

MathML

OAGI

UBL

AECMA 1000D

AECMA 1000D

See here for a couple hundred more: http://xml.coverpages.org/xmlApplications.html

NLM

NLM

NLM

TEI

TEI

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If I don't put the validation information inside the XML instance document, where do I put that information? How do I express the information in a way that is not specific to one schema language?

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First, move validation information out of the XML instance and into

a separate document

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<?xml version="1.0"?><Library> <Books> … </Books> <Employees> … </Employees></Library>

Validation Information

XML Instance

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<?xml version="1.0"?><Library> <Books> … </Books> <Employees> … </Employees></Library>

Validation Information

No validation information in the XML instance document

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<?xml version="1.0"?><Library> <Books> … </Books> <Employees> … </Employees></Library>

Validation Information

Express the validation information in a machine-processable fashion

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<?xml version="1.0"?><Library> <Books> … </Books> <Employees> … </Employees></Library>

Validation Information

Express the validation information in XML!

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<?xml version="1.0"?><Library> <Books> … </Books> <Employees> … </Employees></Library>

Validation Information

Need a standardized XML vocabulary

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Is there a standardized XML vocabulary for expressing validation information, which is also independent of schema language?

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Yes, there is. It's called NVDL.

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NVDL stands for Namespace-based Validation Dispatching Language.

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<?xml version="1.0"?><Library> <Books> … </Books> <Employees> … </Employees></Library>

XML Schema Validator

Relax NG Validator

Schematron Validator

DTD Validator

NVDL Processor

Valid!

NVDL

XML Instance

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Anatomy of an NVDL Script

<rules xmlns="http://purl.oclc.org/dsdl/nvdl/ns/structure/1.0"> <namespace ns="http://www.book.org"> <validate schema="Book.xsd" /> </namespace> <namespace ns="http://www.employee.org"> <validate schema="Employee.xsd" /> </namespace></rules>

See following slides for explanation →

Library.nvdl

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<rules xmlns="http://purl.oclc.org/dsdl/nvdl/ns/structure/1.0"> <namespace ns="http://www.book.org"> <validate schema="Book.xsd" /> </namespace> <namespace ns="http://www.employee.org"> <validate schema="Employee.xsd" /> </namespace></rules>

Library.nvdl

Validate the items in the

http://www.book.org namespace against

Book.xsd

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<rules xmlns="http://purl.oclc.org/dsdl/nvdl/ns/structure/1.0"> <namespace ns="http://www.book.org"> <validate schema="Book.xsd" /> </namespace> <namespace ns="http://www.employee.org"> <validate schema="Employee.xsd" /> </namespace></rules>

Library.nvdl

Validate the items in the http://www.employee.org

namespace against Employee.xsd

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<rules xmlns="http://purl.oclc.org/dsdl/nvdl/ns/structure/1.0"> <namespace ns="http://www.book.org"> <validate schema="Book.xsd" /> </namespace> <namespace ns="http://www.employee.org"> <validate schema="Employee.xsd" /> </namespace></rules>

Library.nvdl

Standardized XML vocabulary

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<rules xmlns="http://purl.oclc.org/dsdl/nvdl/ns/structure/1.0"> <namespace ns="http://www.book.org"> <validate schema="Book.rng" /> </namespace> <namespace ns="http://www.employee.org"> <validate schema="Employee.xsd" /> </namespace></rules>

Library.nvdl

Validate the items in the book.orgnamespaceagainst a Relax NG schema, and the items in the employee.org namespace against an XML Schema

Wow!

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XML instance

Validation Information

Clean separation between dataand validation information

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Summary

• Oftentimes XML developers embed validation information within their instance documents.

• This may not be a good idea for these reasons:– In the lifecycle of an instance document it may need to be

validated against different schemas. If validation information is embedded in the instance document then the instance document will need to be changed at each stage of the lifecycle. That's costly.

– The embedded validation information is limited to one schema language. You may want to utilize XML vocabularies that were created using different schema languages.

• Recommendations:– Remove validation information from XML instance documents.– Put the validation information into a separate document.– Use a standardized XML vocabulary for expressing validation

information.– NVDL is a standardized XML vocabulary for expressing

validation information. Use NVDL.