RE: [xml-dev] Caution using XML Schema backward- or forward-compatibilit

["Costello, Roger L." <costello@mitre.org>]

Thanks Bryan and David.

I believe that we are all in agreement, but some clarification is
needed to make that apparent:

"My XML Schema is backward-compatible."  That statement only tells us
that the XML Schema can *validate* old instance documents.  It tells us
nothing about whether the semantics or relationships (e.g.
co-constraints) are backward-compatible.  Thus, XML Schema
backward-compatibility tells us nothing about whether an application
which is implemented to process instance documents conforming to the
new XML Schema can *process* old instance documents.

Accordingly, I am raising caution to the common fallacy: "If my XML
Schema is backward-compatible then my application can process old
instance documents."

Do you agree?

/Roger 



 

-----Original Message-----
From: David Carver [mailto:d_a_carver@yahoo.com] 
Sent: Wednesday, December 26, 2007 3:06 PM
To: bryan rasmussen
Cc: Costello, Roger L.; xml-dev@lists.xml.org
Subject: Re: [xml-dev] Caution using XML Schema backward- or
forward-compatibility as a versioning strategy for data exchange

bryan rasmussen wrote:
> Well, I think changing the semantics of elements falls outside the
> normal understanding of compatibility.
>
>   
I agree...if you change the meaning of an element, you have broken 
forward compatibility.   Forward compatibility for any grammar has to 
take into account not only the data in the elements, but the semantic 
definition of what those elements mean.