Re: [xml-dev] Schematron Best Practice: A Schematron schema's area of re

["bryan rasmussen" <rasmussen.bryan@gmail.com>]

Well, questions to ask about languages when they are equivalent in
abilities are which one would it be easiest to implement it in. Which
one would be easiest to maintain and extend.

one might be able to put this kind of co-constraint thing into a
grammar based language but you would tie yourself in knots to do it.
it would make your grammar based language difficult to maintain, just
as doing many grammar things in schematron would make it difficult to
maintain.

cheers,
Bryan Rasmussen

On 6/28/07, Costello, Roger L. <costello@mitre.org> wrote:
> ISSUE
>
> When implementing an XML instance document's set of constraints, what
> is a Schematron schema's area of responsibility?
>
> EXAMPLE
>
> Consider this XML instance document:
>
> <?xml version="1.0"?>
> <Document classification="secret">
>     <Para classification="unclassified">
>           One if by land, two if by sea;
>     </Para>
> </Document>
>
> Schematron is very well-suited for implementing this co-constraint:
>
> Security Classification Policy: For the instance document to be valid
> no <Para> element may have a classification value higher than the
> <Document>'s classification value.
>
> The implementation of this co-constraint is shown at the bottom of this
> message.
>
> RESPONSIBILITY OF A SCHEMATRON SCHEMA
>
> The implementation makes some assumptions.  For example, it assumes
> that the classification attributes have already been verified to have
> legal values (top-secret, secret, confidential, and unclassified).
>
> The Schematron schema *could* validate that the classification
> attributes have legal values.  But so could a grammar-based schema
> language (e.g. Relax NG, XML Schema).
>
> QUESTIONS
>
> 1. What is the responsibility of a Schematron schema?
>
> 2. Should a Schematron schema implement constraints that could be done
> by a grammar-based schema language?
>
> 3. Should a Schematron schema implement only those constraints which
> cannot be implemented by a grammar-based schema languages such as
> co-constraints, data cardinality checks, and algorithmic checks?
>
> 4. How much intersection should there be between the set of constraints
> implemented by a Schematron schema and the set of constraints
> implemented by a grammar-based schema?
>
> IMPLEMENTATION OF THE SECURITY CLASSIFICATION POLICY
>
>    <sch:pattern name="Security Classification Policy">
>
>       <sch:p>A Para's classification value cannot be more sensitive
>              than the Document's classification value.</sch:p>
>
>       <sch:rule context="Para[@classification='top-secret']">
>
>          <sch:assert test="/Document/@classification='top-secret'">
>              If there is a Para labeled "top-secret" then the Document
>
>              must be labeled top-secret
>          </sch:assert>
>
>       </sch:rule>
>
>       <sch:rule context="Para[@classification='secret']">
>
>          <sch:assert test="(/Document/@classification='top-secret') or
>                            (/Document/@classification='secret')">
>              If there is a Para labeled "secret" then the Document
>              must be labeled either secret or top-secret
>          </sch:assert>
>
>       </sch:rule>
>
>       <sch:rule context="Para[@classification='confidential']">
>
>          <sch:assert test="(/Document/@classification='top-secret') or
>                            (/Document/@classification='secret') or
>                            (/Document/@classification='confidential')">
>              If there is a Para labeled "confidential" then the
> Document
>              must be labeled either confidential, secret or top-secret
>          </sch:assert>
>
>       </sch:rule>
>
>    </sch:pattern>
>
> /Roger
>
>
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