Subject: [XCON] WG Issues with XML Schema

From: "Pete Cordell" <[email-masked]>
Date: Tue, 20 Mar 2007 17:00:50 -0000

I hope this isn't a mis-use of this list, but.....

As you may know, W3C XML Schema is in the process of being extended to 
version 1.1.  I know that XCON started out using XML Schema, but has since 
moved more towards Relax-NG.

I'm hoping that those making that change of direction will share with me 
their motivation for making that decision.  My intention would be, if 
appropriate, to share any gathered opinions with the XSD 1.1 working group 
(probably in some summarized form).  (BTW - Just to be clear, I'm not on the 
WG.)

For example, is XML schema just too difficult to learn?  Is the versioning 
and extensibility of elements, attributes and enumerations too restricted? 
Were there constraints on your syntax that you couldn't (readily) express 
using schema?  What else?

My motivation for doing this is that I feel that the usage scenarios for 
XCON, SIP and other similar IETF style protocols are very different from the 
sorts of use-cases that the majority of the W3C members are familiar with, 
and hence the requirements are under represented.  There's a chance that by 
giving me feedback, XSD 1.1 will do a better job of meeting the needs of 
working groups in the IETF.

I'm interested to hearing from anybody involved in schema work, whether it 
be in XCON, SIP, SIPPING, AVT, some other IETF group, or for private 
purposes.  However, I'm only posting this message to the XCON list in the 
hope this will capture most of the feedback (the membership of the 
previously mentioned groups is probably much the same anyway).

Depending on what you think is appropriate, you can either reply to the 
list, or direct to me.

Many, many thanks for you help in trying to make XSD 1.1. better!

Pete.
--
=============================================
Pete Cordell
Tech-Know-Ware Ltd
for XML to C++ data binding visit
http://www.tech-know-ware.com/lmx/
http://www.codalogic.com/lmx/
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---

From: "Oscar Novo \(JO/LMF\)" <[email-masked]>
Date: Thu, 22 Mar 2007 13:03:50 +0100

Hi Pete,

I suggest you to read the following e-mail from James Clark:

http://www.imc.org/ietf-xml-use/mail-archive/msg00217.html 

He's the designer of TREX. RELAX NG is based on TREX and RELAX.
I think in this e-mail he explains very well the motivations inside the
IETF to move towards RELAX NG.

Cheers,

Oscar

-----Original Message-----
From: Pete Cordell [mailto:[email-masked]] 
Sent: 20. maaliskuuta 2007 19:01
To: [email-masked]
Subject: [XCON] WG Issues with XML Schema

As you may know, W3C XML Schema is in the process of being extended to
version 1.1.  I know that XCON started out using XML Schema, but has
since moved more towards Relax-NG.

I'm hoping that those making that change of direction will share with me
their motivation for making that decision.  My intention would be, if
appropriate, to share any gathered opinions with the XSD 1.1 working
group (probably in some summarized form).  (BTW - Just to be clear, I'm
not on the
WG.)

For example, is XML schema just too difficult to learn?  Is the
versioning and extensibility of elements, attributes and enumerations
too restricted? 
Were there constraints on your syntax that you couldn't (readily)
express using schema?  What else?

My motivation for doing this is that I feel that the usage scenarios for
XCON, SIP and other similar IETF style protocols are very different from
the sorts of use-cases that the majority of the W3C members are familiar
with, and hence the requirements are under represented.  There's a
chance that by giving me feedback, XSD 1.1 will do a better job of
meeting the needs of working groups in the IETF.

I'm interested to hearing from anybody involved in schema work, whether
it be in XCON, SIP, SIPPING, AVT, some other IETF group, or for private
purposes.  However, I'm only posting this message to the XCON list in
the hope this will capture most of the feedback (the membership of the
previously mentioned groups is probably much the same anyway).

Pete.

---

From: "Pete Cordell" <[email-masked]>
Date: Thu, 22 Mar 2007 13:50:23 -0000

Many thanks for this Oscar.  If I try and summarise each of James' points, 
I'd be interested know which are, say, the top 4 that you (or any one else 
on the list) were most affected by that led you to move away from XSD (I 
hope the focussed input can be of use to the schema working group):

1. XSD requires significant expertise with things like the merging of 
wildcards in attribute groups being counter-intuitive.

2. The XSD spec is hard to understand and not amenable to being easily 
referred to.

3. XSD does not have a formal theoretical basis behind it (whereas RNG 
does).

4. XSD does not have co-constraints, e.g. you can't make element X and 
attribute Y mutually exclusive.

5. The xs:all (analogous to rng's interleave) feature is too weak.

6. XSD's datatypes are not flexible/open enough (and yet saddled with things 
like gMonthDay).

7. An XSD schema can validate seemingly bogus things such as <bogus/> when 
the schema never actually mentions a bogus element (I hope he's wrong about 
this!).

8. Implicitly defined attributes such as xsi:schemaLocation and xsi:type 
conflict with your ability to define the grammer you want.

9. Allowing the specification of default and fixed values is problematic.

And if I can add a few of my own issues:

10. The rules for wildcards (xs:any) conflicting with element names can make 
versioning of a schema from V1 to V2 problematic.

11. Enumerations are not readily extensible.

12. There's no modularity in the schema definitions such that schema B can 
precisely add extensions to a core schema A.

Many, many thanks,

Pete.

----- Original Message ----- 
From: "Oscar Novo (JO/LMF)" <[email-masked]>
To: "Pete Cordell" <[email-masked]>; <[email-masked]>
Sent: Thursday, March 22, 2007 12:03 PM
Subject: RE: [XCON] WG Issues with XML Schema

Hi Pete,

Cheers,

Oscar

-----Original Message-----
From: Pete Cordell [mailto:[email-masked]]
Sent: 20. maaliskuuta 2007 19:01
To: [email-masked]
Subject: [XCON] WG Issues with XML Schema

Pete.

---

From: "Oscar Novo \(JO/LMF\)" <[email-masked]>
Date: Thu, 22 Mar 2007 15:29:45 +0100

Actually, one of the problems we had was with the extensibility of the
schema. Here you have an email from Jari Urpalainen explaining the
issue:

http://www1.ietf.org/mail-archive/web/xcon/current/msg01527.html

Other important problems of XML Schema are number 7 (very critical
one!), 2 and 6.

Hope this information will help you!

Oscar 

-----Original Message-----
From: Pete Cordell [mailto:[email-masked]] 
Sent: 22. maaliskuuta 2007 15:50
To: Oscar Novo (JO/LMF); [email-masked]
Subject: Re: [XCON] WG Issues with XML Schema

Many thanks for this Oscar.  If I try and summarise each of James'
points, I'd be interested know which are, say, the top 4 that you (or
any one else on the list) were most affected by that led you to move
away from XSD (I hope the focussed input can be of use to the schema
working group):

6. XSD's datatypes are not flexible/open enough (and yet saddled with
things like gMonthDay).

7. An XSD schema can validate seemingly bogus things such as <bogus/>
when the schema never actually mentions a bogus element (I hope he's
wrong about this!).

9. Allowing the specification of default and fixed values is
problematic.

10. The rules for wildcards (xs:any) conflicting with element names can
make versioning of a schema from V1 to V2 problematic.

12. There's no modularity in the schema definitions such that schema B
can precisely add extensions to a core schema A.

Many, many thanks,

Pete.

----- Original Message -----
From: "Oscar Novo (JO/LMF)" <[email-masked]>
To: "Pete Cordell" <[email-masked]>; <[email-masked]>
Sent: Thursday, March 22, 2007 12:03 PM
Subject: RE: [XCON] WG Issues with XML Schema

Hi Pete,

Cheers,

Oscar

-----Original Message-----
From: Pete Cordell [mailto:[email-masked]]
Sent: 20. maaliskuuta 2007 19:01
To: [email-masked]
Subject: [XCON] WG Issues with XML Schema

Pete.