[xsd-users] RE: Serialisation issue.

[Moss, David R (SELEX Comms) (UK Christchurch)]

Boris,

Comments below.

Cheers
Dave.

Dave Moss
SELEX Communications
Grange Road
Christchurch 
Dorset  BH23 4JE
United Kingdom
Tel: + 44 (0) 1202 404841
Email: david.r.moss at selex-comm.com

> I tend to think it is a general XML Schema design flaw (or limitation)
> rather than a bug in Xerces-C++. The idea is that you need to always
> specify a complete, top-level schema file for a namespace in import
> declarations and schemaLocation attributes. In your case that would
> mean to import test-users.xsd instead of test-user-config.xsd in
> derived-user-config.xsd. There are also a couple of alternative
> solutions:
> 
> 1. Use different namespaces for test-users.xsd and
test-user-config.xsd.
> 
> 2. Instead of specifying schemas in instance documents, you can
>    programmatically load them into Xerces-C++ grammar cache. This way
>    you can make sure that you load schemas in the proper order (i.e.,
>    first test-users.xsd, then derived-user-config.xsd). For more
>    information on how to do this see the following resources:
> 
>    http://www-128.ibm.com/developerworks/webservices/library/x-
> xsdxerc.html
>    http://wiki.codesynthesis.com/Tree/FAQ
> 

[Moss, David R] 

Right. Importing test-users.xsd instead does the job nicely. 

> 
> Since XML Schema identity constraints are based on XPath and XPath
> operates
> in terms of elements and attributes (instead of types), identity
> constraints
> do not work very well with substitution groups where you change
element
> names (they work ok with xsi:type, since the element name stays the
same).
> 
[Moss, David R] 

I thought I'd try again the xsi:type method (see attached files,
ignoring the commented-out bits from the substitution approach), but I'm
getting 'error, unknown element Age' messages when loading the xml
file.... I'm probably suffering from first-day-back stupidity!


> The only way to make it work with substitution groups is to list all
> possible substitutions in the selector:
> 
> xpath="b:TestUserConfig|DerivedUserConfig"
> 
> (Note, you need to use xpath="b:TestUserConfig" since TestUserConfig
is a
> qualified element.)
> 
> This is not very flexible since you have to hard-code all possible
> substitutions. I think the best solution in this case is to scrap XML
> Schema identity constraints altogether and implement the check in the
> code:
> 

[Moss, David R] 

I think I might end up doing this even if the xsi:type approach works as
it's more user-friendly - clients don't have to add
xsi:type="DerivedUserConfig_t" statements to each record in the
database!

Happy New Year :)
 

> hth,
> -boris


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