Re: APIs, messaging

[Francis Norton <francis@redrice.com>]

"W. E. Perry" wrote:
> 
> Francis Norton wrote:
> > We already use XML Schema structured messages to interface between major
> > components, internal and external, of our retail finance systems.
> 
> I believe that this is too fine-grained for communication with arbitrary
> counterparties across the Internet. The business strategy question, of course,
> is whether that is what you want to do.
> 
Not arbitrary, not yet. Why do you think too fine-grained? Because the
semantics of schema elements might change subtly in different business
flows?

> > [b] that XML Schema means that the message can use declarative validation in
> > the comms layer rather than procedural validation in the application (and
> > no, DTDs don't cut it for us)
> 
> IMHO this presumes that the application knows more of the schema, or that the
> schema designer knows more of the application, than I believe is a healthy or
> reasonable assumption in an internetwork topology.
> 
You may have a point. I am generalising from Schemas written for a
single application family to schemas that would interoperate across
entire vertical sectors. But if standard web-service message schemas
evolve, then application developers will program to them. Hmmm.

> > and [c] that XML Schemas will be the units of selection by which industry
> > standard common message structures will evolve.
> 
> I believe that selection by structure, or schematic, is too brittle and
> fine-grained for the limited knowledge of one node by another in the
> internetwork topology. I specifically believe that, over a large population of
> diverse nodes, there will be only a small percentage whose interaction is
> standardized by the structure of the message exchanged.
> 
I'm only referring to the data structure of the message here - for
instance, I can't believe that we won't end up with a standardised
address schema after we've been doing web services for a while, and if
that's possible then anything is!

Francis.