Re: XML vocabulary for expressing constraints?

Rick, could you expand on that? You wrote:

"It [XML] inhibits integrity checking, QA, QC, validation and verification: it retards the progress of the web by excluding webs of data from the sweet spot in favor of single large documents."

I have not yet understood. What inhibition are you thinking of? What exclusion?

I think that XML has amazing properties for exactly this, the validation of complex system state, expressed as a set of distributed documents. XML+XQuery  offer: (a) outstanding addressing capabilities (the magic formula: URI + XPath), (b) outstanding capabilities of aggregation/filtering. Note that (a) and (b) taken together provide us with the possibility to express the "thing", "feature" or "property" to be validated in a uniform way - as sets of information items and their relationships. To accomplish the validation we then have at our command an expression language (XQuery) which operates on those things in a native way.

The change of paradigm I am waiting for is a new perception which sees documents as contributions to a single, homogeneous space of information, I am waiting for a widespread recognition that documents have a dual nature - distinct entities, *and* just part of a homogeneous substrate of information, which is the forest of information items effectively created by the sum total of accessible XML resources. Documents are like a fishnet plus the water (& fish) contained, located in a lake: the information contained, and the information surrounding are part of a homogenous substrate, where the homogeneity is provided by the uniformity of the node model plus the uniformity of the navigation model (XPath).

Oh, we DO need an extension of our concept of "validity", embracing multiple documents. Restricting "validity" to single documents is a limitation which is not any longer natural. It was *the* view when thinking was pre-URL. But we should look forward, not backward. One of the first steps: treating document references as a built-in data type, making it a basic concept of our information model.

So... could you expand on the inappropriateness of XML when it comes to system validation, or to the treatment of distributed information in general?

Hans-Juergen