Information Technology Reference
In-Depth Information
Chapter 5
Engineering Viewpoint
\I'll have the ginger and mango sausage baguette with a latte," said Nigel,
\and I'll pay for all four of us. We will be out on the terrace." This was one
of his favourite places, just a little way upriver from the oce, with a view
across the broad sweep of the reach as it swung south away from the high-level
bridge. They often came here on a Friday after the technical design reviews.
Claire, Alex and Trudy were already walking down the short brick-vaulted
passage leading to the old wharf that now formed the cafe's terrace.
\But if we have a stable middleware, why do we need to create a separate
engineering specication?" asked Trudy, as they settled round one of the
heavy scrubbed wooden tables. \Isn't all the information implied by selection
of the middleware?" \Well," said Alex, \that depends on whether you have
just one middleware, and on how stable you think your middleware choice is.
A few years ago we thought we might use CORBA everywhere, but then web
services and .NET came along. And you are still using much older ubiquitous
platforms in the hardware repair workshop, with little prospect of any change.
Who knows what another ve years of innovation will bring?" \So how does the
creation of another competing specication help?" \It's not direct competition,
because the engineering language is taking a more abstract, architectural view
of how the system is put together. What we want is a roadmap to guide system
maintenance and transition planning if we do need to integrate a different
middleware solution."
\What exactly do you mean by architectural, here?" asked Trudy. \It's
not the same as a system conguration description, is it?" \No. It's more like
a set of templates for solving the various platform problems found at different
points in the configuration; and these solutions will depend on the level of
reliability or robustness needed. Each actual interaction between the objects
in our computational design needs to follow the appropriate prescription."
He looked across the terrace. \Hello, this looks like our order now." The
waiter had come out with a loaded tray, and they were soon all eating. A
tug with two barges worked its way up river, while a commuter ferry headed
rapidly downstream.
After a bit, Claire put down her panini. \So if you want to change the
requirements, you may end up using a dierent template?" Alex nodded.
\Yes, the template selection can often be done by the tool chain, based on
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