Re: [xml-dev] XML vocabulary for expressing constraints?

[Michael Kay <mike@saxonica.com>]

On 11 Dec 2013, at 01:14, Rick Jelliffe <rjelliffe@allette.com.au> wrote:

Michael's comment on the difference between constraints on a document and constraints over a system is acute, but I think it puts the cart before the horse: people are forced to represent their information as a single document because that is the artificial boundary of common schema languages, not the other way around.

In the database world, of course, integrity constraints are typically scoped to the database as a whole.

But the scope can be wider than that. Look at W3C pubrules for examples of constraints: "every namespace must have a namespace document", "the abstract of every document must include a statement of patent policy", "all links must resolve", "must include a list of changes since the previous draft", "must conform to Web Accessibility Guidelines". It may include constraints whose verification is difficult to automate, and constraints that may be satisfied today but no longer satisfied tomorrow.

Michael Kay

Saxonica