Re: [xml-dev] Constraining a Schema

["Imsieke, Gerrit, le-tex" <gerrit.imsieke@le-tex.de>]

I was tacitly assuming that your customer needs /context-dependent/ 
constraints, for example different div/@type attribute values at 
different locations of a TEI document.

If you simply want to throw out elements or attributes wholesale, your 
base schema probably provides hooks for defining them away or making 
them illegal by one of the other means, Schematron, Relax NG include, 
programmatic removal of references or programmatic addition of xs:asserts.

Gerrit

On 16.08.2018 08:20, Imsieke, Gerrit, le-tex wrote:
> Hi John,
>
> As Eric van der Vlist writes, restricting existing schemas that lack 
> fine-grained hooks for everything that possibly needs to be constrained 
> in the future is harder than extending existing schemas:
> http://books.xmlschemata.org/relaxng/relax-CHP-12-SECT-1.html#relax-CHP-12-SECT-1.3 
>
> If you don’t want to modify the base schema, Schematron is the 
> established way to add an orthogonal layer of additional constraints.
>
> Epischema is another, grammar-based approach, in which you 
> simultaneously apply the liberal base schema and a sparse additional 
> schema that only imposes the desired restrictions but otherwise permits 
> any element or attribute:
>
> https://www.xml.com/articles/2017/04/29/epischemas/
> http://archive.xmlprague.cz/2017/files/presentations/epischema/
>
> The examples have been delivered as Relax NG, but it should be possible 
> at least in principle to implement them in XSD 1.1 where you can have 
> sparse co-occurrence constraints through the new xs:any/@notQName 
> attribute.
>
> The main advantage of epischema over Schematron is better content 
> completion that takes into account the additional restrictions – 
> provided that the XML editor allows the association of multiple schemas 
> and that it only suggests what is legal against all associated schemas 
> in a given context. To my knowledge, oXygen XML editor, with the Relax 
> NG schemas bundled into a single NVDL schema, is currently the only tool 
> that supports this approach.
>
> If constraint-compliant content completion is not an issue, or if XSD is 
> the schema language of choice, I suggest an additional Schematron schema 
> or programmatically (by means of XSLT) patching the base XSD in order to 
> add grammatical constraints and/or xs:asserts.
>
> Gerrit
>
>
> On 15.08.2018 23:25, John Dziurlaj wrote:
> > I am working with a schema that is purposely lax (i.e. it may allow 
> > too many occurrences, may contain irrelevant elements, etc.) so that 
> > it can handle a broad range of customer scenarios. I now have a 
> > customer that wants to constrain the schema such that only a subset of 
> > the functionality is available. This subset is expected to validate 
> > against its larger parent. I’ve come up with a number of different 
> > approaches to handle this:
> >
> >  1. Subset schema using available XML tooling. A standalone derivative
> >     will be produced.
> >  2. Create a new schema, referencing the old one, but derive all the
> >     types by restriction.
> >  3. Use XML Assertions
> >  4. Use Schematron
> >  5. Use CAMV
> >
> > My preference is to use a XML Schema native approach (1-3), using XSD 
> > 1.0 only constructs if possible (1-2), as the actual used XML 
> > processor that gets used is outside my control.
> >
> > Does anyone have ideas on a good approach?
> >
> > John Dziurlaj
> >
> > Elections Consultant
> >
> > Hilton Roscoe LLC
> > Cell 330-714-8935 Work/Fax 234-706-6434
--
Gerrit Imsieke
Geschäftsführer / Managing Director
le-tex publishing services GmbH
Weissenfelser Str. 84, 04229 Leipzig, Germany
Phone +49 341 355356 110, Fax +49 341 355356 510
gerrit.imsieke@le-tex.de, http://www.le-tex.de

Registergericht / Commercial Register: Amtsgericht Leipzig
Registernummer / Registration Number: HRB 24930

Geschäftsführer / Managing Directors:
Gerrit Imsieke, Svea Jelonek, Thomas Schmidt