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I've got a general design question that I would like input and maybe
alternate ideas for implementation.
I work for ACORD which is an Insurance industry standards group and we are
updating our DTD spec to now use Schemas. We have an internal need and
philosophy to be able to extend our standard to allow for company unique
information. Our standard covers the common 90% of the need that everyone
can agree is standard and common requirements. So we need someway to allow
the additional 10% to be added by specific vendors and carriers.
We don't want wild card or general namespace capabilities that would allow
any element from any namespace anywhere within our model/design. Instead we
want a very controlled inclusion or exclusion of elements within content
models. So that element newA is only allowed in the ACORD D F and G
elements, but none of the others. We don't want anyone changing the
datatypes of existing ACORD elements, but we do want them to reuse the
elements or aggregates (elements composed of elements) as they want or to
create and use their own elements and aggregates.
The other twist here is that most members are saying they aren't going to
do validation on their production system. They may test with a schema their
for validation, but in production they intend to remove this functionality
and rely on their code to do all the work. We also have everything
currently defined as global elements, there are no local definitions.
Solutions being considered
1) Like Roger Costello'ss Best Practice document, we have had a suggestion
of using the xsd:any and xsd:anyattributes features, but this allows too
much flexability. I can use any element from any allowed namespace to be
used anywhere the 'any' wild card appears.
2) xsd:redefine has also been proposed. I like this idea because it very
specifically indicates what is being changed and it specifies exactly the
changes being made. These changes are managed outside of the original
schema and very explicitly indicates where the modifications have been
made. The issue raised with this is that some of the members don't want the
ACORD namespace and elements being trampled on by other
people/organizations. To me I don't see any problem, the end result is that
I have an exist ACORD element being extended by adding new company
elements, existing ACORD elements, or the removal of ACORD elements and all
of this is managed ultimately with the use of the namespaces and the prefixes.
3) The alternate to #2 is to require the reusing organization to create in
their own namespace the thing they want to modify. The idea being that they
would somehow derive their new object from the ACORD element, give it
essentially the same name in their namespace and then make the
modifications as they needed. So the parent object and any company unique
elements are in the companies namespace and ACORD reused elements would
appear in the ACORD namespace. This new object would then automatically
replace all the definitions of the ACORD element.
Possible Schema Designs
So what we have in the ACORD specification is something like this:
<xsd:element ref="TitlePrefix" minOccurs="0" maxOccurs="1"/>
<xsd:element ref="FamilyNames" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="Surname" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="NameSuffix" minOccurs="0" maxOccurs="1"/>
Now company B wants to add a idCode to this element. So with redefine I
would have something like:
<xsd:element name="idCode" base="xsd:string"/>
<xsd:redefine schemaLocation="acord.xsd" >
<xsd:element ref="A:idCode" minOccurs="0" maxOccurs="1"/>
This one I'm less sure of but the indication seems to be:
1) The elements in the ACORD schema would have to be changed to be based
upon a complexType then that complexType is then used by company A
<xsd:complexType name="FamilyNameType" >
<xsd:element ref="idCode" minOccurs="0" maxOccurs="1"/>
Now doesn't this all still come down to the following schema instance:
Does it really matter which way we use to define the extensions if the
result is the same XML stream?
Does any of this really matter (or is it even allowed) if we aren't using
the schema for validation of every stream in production?
Any other ideas or suggestions?
Who is the definitive source on the different ways of doing things? One
member points to the description in the Schema spec that seems to indicate
that Redefine was only meant to be used when versioning your own schema and
not for combining schemas - is this its only allowed use? It seems to me
that the schema spec has multiple ways/solutions for doing things (for
instance redefine and any) and it is up to the implementor to decide what
fits the problem at hand. If that is true then having suggested uses in the
spec that look like restrictions rather than suggested applications is a