Re: [xml-dev] Data versioning strategy: address semantic, relationship,a

[David Carver <d_a_carver@yahoo.com>]

The versioning strategy is also going to change on your perspective and 
use of what is being developed.   From an XML Schema standpoint which I 
deal with a lot.  Backwards compatibility to me is when an older 
instance can still validate a against a newer schema (really forwards 
compatible).   However, a use may have a different view point, as they 
may be doing data binding, and just because the newer schema can 
validate an older instance, the code that they generate from that newer 
schema may generate totally different classes.

So versioning, you really have to narrow the scope of what you are going 
to talk about when versioning, as it changes based on your perspective 
and use of what is being versioned.



bryan rasmussen wrote:
> I think a versioning strategy must in the initial formulation of the
> strategy specify how applications that support the format should react
> to new versions. This could conceivably be not just the ways outlined
> but also algorithms for determining if the new version is compatible
> with older versions, or lookups of new validations etc. of an external
> repository for the new version.
>
> A versioning strategy is, with this view, a contract on the relation
> between different versions of the format. As such it is harder to
> change the versioning strategy than it is to change the format itself,
> it is at a higher level of control.
>
> Cheers,
> Bryan Rasmussen
>
> On Dec 7, 2007 9:55 PM, Costello, Roger L. <costello@mitre.org> wrote:
>   
>> 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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>>     
>
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