RE: [ws-caf] Context - XML technical

["Tony Fletcher" <tony_fletcher@btopenworld.com>]

Dear Kevin and others,

I will stay neutral on whether it makes sense to generically identify
contexts or not - but just in case it does I would like to suggest a
technical XML mechanism that I think allows fore this whilst still forcing
the actual context structure used to be defined in a referencing
specification.

I was unaware that a type could be made abstract (in XML) as well as an
element until I looked up the XML Schema primer the other day to remind
myself about the use of abstract elements.

It appears to me (and I am open to correction) that if we define a context
element and make its type abstract (rather than making the context element
abstract), then an instance document will identify the context with the
context namespace prefix (such as wsctx:context assuming that that prefix is
declared with an xmlns 'declaration' but will have to include an xsi:type
attribute that points to the type in the schema where that type is defined
(need not be the context schema, and will not be if we do not define any
suitable types in the context schema).  This approach should mean that we
can define where the context headers go in the WSDL for context services and
clients but leave open the definition of the precise (extended) structure.
So change the schema to:

<xs:complexType name="ContextType" abstract="true">
		...
<xs:element name="context" type="tns:ContextType"/>

A thought for others to investigate further perhaps.  If it does work maybe
we should make this change anyway independent of other discussions.

Best Regards     Tony
A M Fletcher
Tel: +44 (0) 1473 729537   Mobile: +44 (0) 7801 948219
 tony.fletcher@choreology.com    amfletcher@iee.org       (also
tony_fletcher@btopenworld.com)
 


-----Original Message-----
From: Kevin Conner [mailto:Kevin.Conner@arjuna.com] 
Sent: 17 June 2005 09:44
To: Tony Fletcher
Cc: ws-caf@lists.oasis-open.org
Subject: Re: [ws-caf] Context query


Hiya Tony.
...
> I would like to explore the technical changes made / we are making, to 
> make sure that I (and perhaps others) know about them and understand 
> their implications.
> 
> In the version of the Context schema that you sent me as being a 
> latter revision than the currently available one, the context element 
> is still present but now defined as being abstract.
> 
> <xs:element name="context" type="tns:ContextType" abstract="true"/>
> 
> Some questions/points:
> 1)  Why is the context element made abstract rather than the context 
> complexType?

The only effect of making the context type abstract is to force a
referencing specification to define a sub type.  I do not believe this was
the intention of the resolution but am willing to change it if others
disagree.
- Kevin