RE: Open Content Model

XSLT also has an essentially open content model, which has proved both
useful and harmless.

 

On the other hand, XML Schema does not provide such an open content
model.  As far as I can tell, it only allows attribute extensibility on
a few elements, and limits element extensibility to the <xs:annotation>
element.  Personally, I never understood this decision.  It appears
overly complex and cumbersome.  Does anyone have any knowledge of the
rationale for this design?

 

-----Original Message-----
From: Keith Ballinger [mailto:keithba@microsoft.com] 
Sent: Monday, April 22, 2002 7:07 PM
To: www-ws-desc@w3.org
Subject: Open Content Model

 

One item I've had on my plate is to describe why the open content model
is something we should try to take advantage of as much as possible with
the WDSL revision. 

 

To begin with, when I say open content model, I mostly mean allowing
extra element and attributes from other namespaces within a schema. This
is typically done with the <any/> and <anyAttribute/> schema tags. These
elements also allow you to specify which namespace (including ##other,
which means any namespace but the one in the schema), as well as the
default processing of these elements. An example of this can be found
with the <binding> element in WSDL today. This element allows child
elements of the type: <any namespace="##other" minOccurs="0"
maxOccurs="unbounded" />

 

Working with SOAP and WSDL over the past few years has shown me the
value in allowing this open content model. It is very useful especially
for extending a specification in new ways. As authors of specs, we may
cover many use cases and requirements in a first class way, but we need
to provide for those other requirements that come to us that we don't
anticipate. The open content model allows us to handle many of these. 

 

I would also recommend that we keep WSDLs mustUnderstand feature for
extensions, the wsdl:required attribute.

 

As a matter of technique, I feel that we should be overly open as
opposed to overly closed. This would lead to putting this open content
model on all elements, and then finding reasons why it shouldn't be on
one. 

 

Cheers,

Keith