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Re: [xml-dev] RE: Caution using XML Schema backward- or forward-c ompatibility as a versioning strategy for data exchange

From: "bryan rasmussen" <rasmussen.bryan@-----.--->
To: "Len Bullard" <len.bullard@---.--->
Date: 1/2/2008 9:15:00 PM
>
> When you say 'interoperability', you open a very deep can of system worms.
> As has been asked many times on this list, what do you mean by
> 'interoperability'?  Last time I asked, the reply I got was something along
> the lines of "well, Len, we ALL know what we mean by that; we don't have to
> define it" but that sort of punt doesn't work in a standard and that
> assumption is specious.   My reply is still, "Data is portable.  Systems
> interoperate".  Without a systemic definition, a standard promising
> "interoperability" is guaranteed to fail without out-of-band definitions.
> Without consolidation into a process-mediated contract/standard/spec, the
> drift is inevitable.  So now it comes down to the size of the system, its
> role among systems of systems, and the different gaps emerging from
> unforeseen applications of these.
>
Data is portable. Systems interoperate. That seems a good starting
point for defining what interoperability is; how about:

Interoperability can be said to exist in an exchange between systems
when two parties managing systems that exchange and process data in an
pre-agreed upon manner are also in agreement that the exchange and
processing of the data is proceeding in the manner that was previously
agreed upon. By this definition one sees that interoperability, as so
many things are, exists in portions of a complex system.

To determine the state of interoperability in a complex network of
many parties there are different methods:

1.  The internal network report: The degree of interoperability
between any two systems in a series of exchanges is measured by the
agreement of the parties managing the systems as to what portions of
the exchange are functioning correctly; the data from all systems that
return this data for measurement can be used to determine the general
state of interoperability in the system.

The factors of any interoperability measure is then: when does the
network interoperate, when does it fail to interoperate, how much data
about interoperability of the network are we missing?

2. The external network report: In many modern networks where
interoperability is supposed to be taking place the internal network
report is of little use, this can be for the following reasons: There
is too much interoperability data missing for a reasonable analysis,
the parties managing the systems that are doing the exchanges cannot
reliably be ascertained or queried as to the interoperability of their
systems, or there is no agreed upon system for putting the internal
network report into action.

In such a system interoperability cannot directly be determined but
rather the chance that interoperability exists can be evaluated (with
much argument and discussion as to the meaning of the evaluations),
such a method involves inspection of the transports between the
systems and examination of the data against an agreed upon set of
standards that are supposed to achieve interoperability. In the cases
where the data moving between the systems match specified requirements
for that data it is assumed that there is a high chance of
interoperability, in the cases where the data does not match specified
requirements it is assumed that there is a less chance of
interoperability, in the cases where it can not be accurately
determined if the data matches or does not match there is an unknown
chance of interoperability. This method can be, with lots of
data-crunching power and with abilities to determine specifically what
systems on the network are responsible for what data being
exchanged[this second is not always doable in many types of networks],
used to determine the chance of interoperability in two systems,
including the chance of interoperability of two systems on the network
that have as yet not exchanged data.


The first may exist in an efficiently managed company. The second is I
believe somewhat regularly, if imperfectly, implemented. Obviously one
would prefer to determine the actual interoperability among the
systems that take part in a network for data exchange, but most often
we can only determine the chance of interoperability.

Cheers,
Bryan Rasmussen

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