Re: Simplifying XML Schema

Philip Wadler wrote:

> Ashok,
>
> Thanks for your message, sorry to be so long in replying (all free
> time has gone to hammering out the algebra).
>
> You suggest that xsi:type might be useful in data integration.
> (In fact, the same point had occurred to me, so I am softening
> a little with regard to xsi:type.)  However, I'm confused by one
> thing.  Here's the last example you give:
>
>   <authors>
>     <author xsi:type='firstAuthor'>Peter Buneman</author>
>     <author xsi:type='secondAuthor'><first>Dan</first><last>Suciu</last><author>
>   <authors>
>
> Does this work in Schema?  I thought that Schema disallowed two
> sibling elements to have the same name but different types.

It's valid if <author> is declared with type 'anAuthor'
from which both 'firstAuthor' and 'secondAuthor' are
derived.

I believe this approach had been proposed with 'anAuthor'
as an abstract type.  Of course, it's a bit clumsy but
saves extending XML Schema if it is adequate for a possibly
unusual use case.

Thanks,

  David