RE: [xml-dev] Stability of schemas -- frequency of versioning

[<w3c@drrw.info>]

Roger,

This is but one reason of many that people are preferring to use CAM templates for validation.

1) CAM has dynamic structure constructs so you can accommodate variants in what your information exchange partners are doing - e.g. 500 trading partners sending what they think is valid XML per schema - you can handle that with ONE template

2) CAM is fault tolerant - it issues warnings and errors - so your processing does not fail and break

3) It can do extended checking and validations that schema alone cannot

4) It has SQL table lookups so you can check dynamic data - customer numbers, part numbers, etc.

5) It uses dictionary collections so you can align your component definitions across schema collections

See working examples and more - http://www.cameditor.org

Enjoy, DW

-------- Original Message --------
Subject: [xml-dev] Stability of schemas -- frequency of versioning
From: "Costello, Roger L." <costello@mitre.org>
Date: Mon, November 21, 2011 7:58 am
To: "xml-dev@lists.xml.org" <xml-dev@lists.xml.org>

Hi Folks,

How frequently should schemas be allowed to change?

Let "schemas" refer to XML Schema, Relax NG, DTD, or Schematron.

Let "change" refer to non-backward compatible changes such as requiring a new element.

I will attempt to persuade you of the following:

To be effectively deployed, schemas require a certain amount of stability.
That is, they shouldn't change too often. Further, any changes that do occur
should be backward compatible.

That says, for example, that if your domain is Books then the kind of information that goes into Books is stable; if your domain is financial contracts -- swaps, options, futures -- then the kind of information that goes into financial contracts is stable. Consequently your schemas are stable. Conversely, if your Book or financial contract schemas are constantly changing then your schema development and software development will thrash and users will be constantly confused.

An example of a rock-solid schema is the XML Schema for XML Schemas. It hasn't changed in 10 years. And the new version is backward compatible with the old. Ditto for the Relax NG schema for Relax NG schemas.

Suppose, however, that the information for a domain is required to frequently change, say, three times a year. I have attempted to persuade you that a schema may not be a good fit for describing that type of information. But I am at a loss for what is a good fit. What is a good fit?

/Roger

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