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My perspective is that any schema language is a constraint language. When you say "Determining if an instance is valid is a matter of checking that the instance adheres to the specification." I would say "Determining if an instance is valid is a matter of checking that the instance does not violate any of the schema's constraints." And one can say "An authoring tool directs the creation of content that does not violate any of the schema's constraints". Different uses put different spins on the activity, but at the core is the activity is guided by sets of constraints. That way you can have many sets of constraints using different technologies (W3C XML Schema, Schematron, etc.), and then selectively decide if an instance is valid against any or all sets of constraints. RELAX-NG and DTDs define constraints as pattern grammars, W3C XML Schema defines constraints as type hierarchies, and Schematron defines constraints as content assertions. Horses for courses. I hope this helps. . . . . . . Ken At 2021-04-21 12:23 +0000, Roger L Costello wrote: Hi Folks, -- Contact info, blog, articles, etc. http://www.CraneSoftwrights.com/x/ | Check our site for free XML, XSLT, XSL-FO and UBL developer resources | Streaming hands-on XSLT/XPath 2 training class @US$125 (5 hours free) | Essays (UBL, XML, etc.) http://www.linkedin.com/today/author/gkholman | [Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] |
