Fw: [dfdl-wg] Annotation complexity
Steve Hanson
smh at uk.ibm.com
Thu Dec 2 04:08:01 CST 2004
Some thoughts on this from one of the IBMers on the XML schema WG.
Regards, Steve
Steve Hanson
WebSphere Business Integration Brokers,
IBM Hursley, England
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 02/12/2004 10:05 -----
Sandy
Gao/Toronto/IBM at I
BMCA To
Steve Hanson/UK/IBM at IBMGB
30/11/2004 14:58 cc
Suman Kalia/Toronto/IBM at IBMCA
Subject
Re: Fw: [dfdl-wg] Annotation
complexity(Document link: Steve
Hanson)
> One more thought in this area. XML Schema itself does not have the notion
of inheriting properties from a parent object.
I think by "parent object" you mean the containing component, instead of
something like the "base type".
I don't think schema has a general principle on this. The only case I can
think of where things are inherited (or defaulted using values from parent)
is for blockDefault, finalDefault, elementFormDefault and
attributeFormDefault attributes on the <schema> element.
As for your specific example, I don't know whether the Schema WG has
considered it (my involvement in schema doesn't go that far back), but my
intuition here is that I don't think that's something schema would want to
do. I think defaults are for the common cases, but it's not that common for
all elements inside a complex type to share the same type.
Don't know whether that answered your question. Let me know if there's
anything more I can do.
Cheers,
Sandy Gao
Software Developer, IBM Canada
(1-905) 413-3255
sandygao at ca.ibm.com
----- Forwarded by Steve Hanson/UK/IBM on 30/11/2004 11:39 -----
Steve
Hanson/UK/IBM
To
23/11/2004 09:38 Sandy Gao/Toronto/IBM
cc
Suman Kalia/Toronto/IBM at IBMCA
Subject
Fw: [dfdl-wg] Annotation complexity
Hi Sandy
There is a Global Grid Forum (GGF) initiative underway called Data Format
Description Language (DFDL) which aims to model non-XML data using XML
schema for the logical structure and xsd:appinfo annotations for the
physical 'bitstream' representation information. IBM is involved in this
(myself and Suman Kalia) because the IBM message broker product (WVBI-MB)
already does exactly this in its 'message model', so we are using our
experience in this area to help influence this initiative.
I'd like to ask your opinion on something quite specific. See the mail
directly below. Did the XML Schema WG think about the possibility of
providing an inheritance or defaulting capability as in my example? And if
so, what were the precise reasons for excluding it? I'm asking because
several folk in the DFDL WG are keen on having this as a way of making a
DFDL annotated schema more compact.
If you are interested in finding out more, please visit
http://forge.gridforum.org/projects/dfdl-wg/
Regards, Steve
Steve Hanson
WebSphere Business Integration Brokers,
IBM Hursley, England
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 23/11/2004 09:30 -----
Steve
Hanson/UK/IBM
To
23/11/2004 09:29 dfdl-wg at gridforum.org
cc
Subject
Fw: [dfdl-wg] Annotation complexity
One more thought in this area. XML Schema itself does not have the notion
of inheriting properties from a parent object. For example, if I have a
complex type that contains only integer elements, there is no facility to
factor out the xsd:type attribute from all the elements and instead set it
as an attribute of the complex type, thereby making the schema more
compact. Was this a deliberate decision? I'll see if I can find out.
Regards, Steve
Steve Hanson
WebSphere Business Integration Brokers,
IBM Hursley, England
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 23/11/2004 09:27 -----
Steve
Hanson/UK/IBM
To
22/11/2004 11:24 dfdl-wg at gridforum.org
cc
Subject
RE: [dfdl-wg] Annotation complexity
(Document link: Steve Hanson)
> Another approach would be to allow annotation locations to be
> specified using XPath. Since XPath can specify both specific
> locations and large groups of locations this could be quite
> powerful.
We used to have a similar concept in the IBM broker message model, we
called it 'element qualifier'. A top level global element could carry a
reference (XPATH) to an element it ultimately contained, for the purposes
of overriding certain properties, including default value. We found that:
a) Their use made the model much harder to understand
b) The code we had to write was considerably more complex
c) No customer ever admitted to using the capability
We withdrew the facility with no deprecation warning in V5 (June 2003) and
so far nobody has shouted.
Was this the kind of thing you are proposing?
Regards, Steve
Steve Hanson
WebSphere Business Integration Brokers,
IBM Hursley, England
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848
"Myers, James D"
<jim.myers at pnl.go
v> To
Sent by: dfdl-wg at gridforum.org
owner-dfdl-wg at ggf cc
.org
Subject
RE: [dfdl-wg] Annotation complexity
19/11/2004 21:03
>
> Myers, James D wrote:
> > I guess I'm not sure how restricting annotations to elements solves
> > things.
>
> Sorry, I am finding it more difficult to be precise than I
> thought with
> this. What I mean here is _leaf_ elements/attributes - which
> I think can
> be defined as elements with simple type descriptions. I think if you
> stick to these its unambiguous...no?
I agree, I think - if anotations are only on simple types. That would
eliminate the element hierarchy, though - does it eliminate the type
hierarchy - simple element in base type has an annotation that gets
inherited by the same simple element in a derived type. I think this
would be unambiguous, but perhaps hard to find (surprise the global dfdl
default for endianess doesn't apply because some subtype three levels
back had an annotation)
>
> I think Mike has examples of annotations that he would like higher in
> the tree but with this extreme position there would be no inheritance.
Except through type derivation...?
>
> Two other thoughts occur:
> - I think definitions applied to a data source are
> orthogonal to this
> scoping issue. We still need to understand precedence but that seems
> relatively easy to resolve.
Definitions on sources: I know we've talked about this (!!! - the whole
outside-in or inside out representations...), but I think the only
mechanism for this in the examples is to assign a source to an element
and annotate that element with, for example, endianness. For some types
of sources, e.g. other layers, that have an internal structure, any
annotation of the source itself would essentially become an inheritable
annotation on the elements within it. So - we could try to define such a
mechanism to apply to sources, but I'm not sure it would be applicable
to all without recreating some of the inheritance issues.
>
> - Another approach would be to allow annotation locations to be
> specified using XPath. Since XPath can specify both specific
> locations
> and large groups of locations this could be quite powerful.
Hmmm. Yes, as long as xpaths can only be defined from a single root,
i.e. not from within type definitions relative to the type (not talking
about layers here). Otherwise we don't get rid of inheritance/precedence
issues. At a minimum, this approach might help collect all of the
defaults together at the top level for readability, but it might
separate defaults from reusable types.
Jim
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