Dear John, (01)
> >> Ultimately, the test of the Semantic Web--and the applications that
> >> we build for it--will be the extent to which applications built by
> >> others interoperate with ours.
> > That is broadly what I understand by interoperability too. However, I
> > see interoperability at two levels, which I will describe as weak
> > interoperability and strong interoperability.
> > Weak interoperability is when each system that is interoperating is
> > completely independent, and interfaces are negotiated between systems
> > that need to operate on a one-to-one basis, and may involve extensive
> > mapping between different coding systems. The problem with weak
> > interoperability is its fragility.
> This is vague. Please give one or more examples of implemented and
> systems that use what you call 'weak interoperability' and show how they
> down because of the "fragility". (02)
MW: I'm surprised you are not familiar with what I am describing, even if
not with the terms.
When enterprises first started out noticing that it would be convenient to
share information between two systems, they started building interfaces
between them. These were sometimes described as point-to-point interfaces.
After a while it was noticed that these interfaces were becoming a major
part of the cost of new systems. In the 90's Shell somewhere quoted a figure
of 70% of the cost of new systems was the cost of interfacing them to
existing systems. These interfaces where fragile because a change in any one
of (hundreds to thousands) of systems could impact tens of interfaces, and
with thousands of interfaces and the pace of development of new systems, the
burden of keeping up more or less ground things to a halt. This is the
situation that I describe as weak interoperability.
> > In a medium to large network of systems (say 20+) this can be very
> > costly. However, this is what TBL seems to be advocating.
> I didn't see anything in Tim's proposal that has any resemblance to what
> said above. Could you relate his exact words to the implemented examples
> what you call "weak interoperability"? (03)
MW: If the systems and the interfaces between them are essentially
independent, then you can only have this situation. It is the only one that
gives you the "freedom" suggested. It would be good if I were mistaken, but
can you point to where it is necessarily strong interoperability that is
> >> As an example, I cited the Amazon.com database schema, which is
> >> highly underspecified. But it enables vendors around the world to
> >> interoperate with the Amazon software in describing, selling, and
> >> shipping a wide variety of products.
> > I would not describe this as underspecified, just focused. I think you
> > will find it is quite precisely specified in things like delivery
> > addresses, credit card details, product pricing, delivery charges,
> names, etc.
> It's underspecified in the sense that the product categories -- such as
> electronics, cameras, toys -- are not defined. (04)
MW: Yes they are! Have you looked at Amazon recently, this is just how the
store is divided up!
> > Indeed, but if those limited semantics are not true always and
> > everywhere there will be occasions when their systems cannot be used
> > (or fudge/false data will have to be used to make them work).
> Different vendors might classify similar things as toys, electronics, or
> cameras. Such discrepancies might cause a vendor to lose sales, but they
> won't cause any system (Amazon's or any vendor's) to crash. (05)
MW: But it could have an effect on whether you make any sales of a product
if it is misclassified (unless it can be multiply classified). (06)
> The current methods are adequate to support a multi-billion dollar
> The penalty of losing sales is sufficient to cause vendors to keep their
> classifications reasonably consistent with one another. (07)
MW: Well they are just conforming to the high level classifications that
Amazon have defined as best they can. Not that I am suggesting they have got
this particularly wrong, but no vendor is inventing "electronics" as a
> These methods actually work. That's more than one can claim for most
> ontologies and tools for building and/or using ontologies. (08)
MW: I also expect that Amazon is quite aware of new product categories as
they emerge, and will elaborate and prune the root classification schemes
they use to help that.
> > Strong interoperability replaces this point-to-point approach with a
> > hub-and-spoke approach. So, you still have independent applications,
> > but now there is a central hub (which may be virtual) with an
> > overarching ontology and a single coding system. Interfaces are now
> > just to and from this central hub, and preferably, all the systems use
> same coding system.
> Precise standards are needed for many purposes. That point was recognized
> 14th century, and it has become increasingly important in science,
> engineering, business, and finance ever since.
> But note that the question of how ontologies and standards are or should
> related is still an active topic of debate. (09)
MW: It is quite straight forward. For data exchange to be successful there
needs to be an agreement about what the meaning is of what is exchanged.
That is an ontology, and it is a standard. End of debate. (010)
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