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

[Frank Manola <fmanola@acm.org>]

+1 to what Michael Kay said.  Clearly this is going to be application-dependent.  If it's worth more to have a modified schema than the cost of doing the modification, then you'll do it.  Look at US government applications and forms that are based on laws passed by Congress and associated regulations issued by government agencies.  The laws and regulations change all the time, and try telling Congress that everything has to be "backward compatible"!  That had better not mean you can't use XML schemas for those purposes (or a lot of people who read this forum would be out of business).

On Nov 21, 2011, at 7:58 AM, Costello, Roger L. wrote:

> 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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