xml-dev - Re: Different schemas....

[Rick JELLIFFE <ricko@geotempo.com>]

> Pamela Rais wrote:
 
> Are there other such deviations from the Schema proposal out there?
> If so, what are they?

Probably all of them!
 
> I'd appreciate any info that can enlighten me. I'm making the jump
> from SGML/DTD's and it seems quite daunting.

W3C XML Schemas is currently nearing the end of a long (more than 18
months) development, from basic designs prepared 3 years ago.  It is
currently at "Last Call" draft stage. So any implementation of XML
Schemas is only a draft implementation.  In fact, there is no such thing
as an implementation of XML Schemas, only implementations of specific
drafts!

The head of each draft gives a paragraph clearly indicating its status
as draft. See http://www.w3.org/TR/ 

For the most recent draft:

"though the Working Group does not anticipate further changes to the
functionality described here, this is still a working draft,            
subject to change. The present version should be implemented only by
those interested in providing a check on its design or by            
those preparing for an implementation of the Candidate Recommendation.
The Schema WG will not allow early implementation to            
constrain its ability to make changes to this specification prior to
final release."

This should be taken seriously!  Obviously the XML Schema WG will be
very loath to change things after the 6 public drafts.  However, some
things will change.  People should not expect any current schema format
which might claim to be a subset of XML Schemas to port instantly: the
namespace may change slightly, the element or attribute names may change
slightly, intermediate elements may be put in or elements coalesced,
some things may be made more regular, some features may be somewhat
reworked, some new features may be required.  

The XML community and the various stakeholders have recently been
gratifyingly active in commenting on the draft. This is excellent news
(I had been concerned before that people were more interested in banning
comment delimiters than bringing out XML's capabilities); XML Schemas
will determine the idioms and capabilities of the 2001 generation of XML
products--it will be the face of XML for people from the database world
in particular. So it is very important it has serious and hard review. 

However, you can expect the general framework of XML Schemas and the
lion's share of the specifics to remain unaltered.  Don't expect
features to disappear.

(Boring: The next formal steps for XML Schemas is to move to Candidate
Recommendation for several months, to allow feedback from implementers
and stakeholders. Then it becomes a Proposed Recommendation of W3C then
a Recommendation shortly after that.  I mentioned yesterday that there
may be another Last Call draft, but please that is an opinion, not an
announcement.)

However the current draft is certainly stable enough to start developing
schemas with. Don't forget that you will have a bit of time before XML
Schema tools appear and are mature, perhaps 1Q/2001 is a prudent time to
target.  Don't plan as if XML Schemas is final now!  

(Please, I hope that XML-DEV does not take this as some foreshadowing of
particular changes coming.)

Rick Jelliffe

(Member, W3C XML Schema WG, writing in private capacity)