Hi Roger,

I typically collapse the relationship and syntax changes into one because they come down to the same, that is they both contribute
to determining whether an instance is in a version of a language.  I 100% agree that a versioning strategy must cover syntax,
relationships, and semantics.  

The W3C Technical Architecture Group has been working on this for a long time.  We have been using the Accept and Defined Text Sets
and the Information Set (not the XML kind) conveyed by a text of the language.  The terminology section shows these terms,
relationships and more.  Our latest draft thoughts are:
- strategies on how to achieve compatible versioning in a language: http://www.w3.org/2001/tag/doc/versioning-strategies
- terminology for versioning: http://www.w3.org/2001/tag/doc/versioning
- xml and xml schema designs for versioning: http://www.w3.org/2001/tag/doc/versioning-xml

Your thoughts and reviews are appreciated.

Cheers,
Dave

> -----Original Message-----
> From: Costello, Roger L. [mailto:costello@m...] 
> Sent: Friday, December 07, 2007 12:55 PM
> To: xml-dev@l...
> Subject: [xml-dev] Data versioning strategy: address 
> semantic, relationship, and syntactic changes?
> 
> Hi Folks,
> 
> Oftentimes when discussing a "versioning strategy" I focus on 
> how to design schemas in a fashion to lessen the impact of 
> changes.  It occurs to me that this addresses only one aspect 
> of the data versioning problem.  Below I have attempted to 
> identify other issues to be addressed in a data versioning 
> strategy.  I am interested in hearing your thoughts on this.
> 
> EVOLVING DATA
> 
> Suppose some data is regularly exchanged between machines:
> 
> Machine 1 --> data --> Machine 2
> Machine 1 <-- data <-- Machine 2
> 
> Periodically the data changes due to requirement changes, 
> additional insights, or from innovation. 
> 
> A change results in a new "version" of the data.
>  
> 
> PROBLEM
> 
> What are the categories of changes that may occur?  What 
> categories of changes must be dealt with by a data versioning 
> strategy?
> 
> 
> CATEGORIES OF CHANGE
>  
> 1. Semantic - the meaning of the data changes.
> 
> Example: 
> 
> version 1 data: a "distance" value means the distance from 
> the center of town. 
> 
> version 2 data: a distance value means the distance from the 
> town line.
> 
> 2. Relationship - the relationship between the data changes.
> 
> Example: 
> 
> version 1 data: there is a co-constraint between the 
> start-time and the end-time.  
>          
> version 2 data: there is a three-way co-constraint between 
> start-time, end-time, and mode-of-transportation.
> 
> 3. Syntax - the structure of the data changes.
> 
> Example: 
> 
> version 1 data: the employee data is listed first and the 
> person's name is given by his given-name and surname.
>          
> version 2 data: the department data is listed first and in 
> the employee data each person's name additionally contains a 
> middle name.
> 
> 
> SUPPORTING TECHNOLOGIES
> 
> Suppose the data being exchanged is formatted using the XML syntax.  
> 
> Machine 1 --> XML --> Machine 2
> Machine 1 <-- XML <-- Machine 2
> 
> What technologies support the above categories of change?
> 
> 1. Semantic: A data dictionary may be used to define meaning.
> 
> 2. Relationship: Schematron may be used to express 
> relationships between data.
> 
> 3. Syntax: XML Schema, Relax NG, or DTD may be used to 
> express the structure of the data.
> 
> 
> REQUIREMENTS ON A VERSIONING STRATEGY
> 
> A versioning strategy must take into consideration:
> 
> - changes in the semantics of the data
> - changes in the relationships of the data
> - changes in the syntax of the data
> 
> When data is in an XML format then a versioning strategy must
> implement:
> 
> - versioning a data dictionary
> - versioning a Schematron schema
> - versioning an XML Schema, Relax NG schema, or DTD
>  
> 
> QUESTIONS
> 
> a. Do you agree with the three categories of change?  
> 
> b. Do these categories represent all types of change?
> 
> c. Do you agree that a versioning strategy must address 
> semantic, relationship, and syntactic changes?
> 
> /Roger
> 
> 
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