I think in practice Tim's number is correct. The division by two
works only if both parties agree on a standard interface for
sending/receiving.
In practice, senders tend not to bother, unless that means moving to
a standard. Receivers have to deal with what they get - ie two
interfaces between two parties.
Ian.
At 3:13 pm +1100 12/3/06, Tim Churches wrote:
Paul Clarke wrote:
Hi Tim,
Your point on the number of interfaces is quite correct, however I think
the formula should be:
For n systems, where n> 1, the number of interfaces is : n(n-1)/2
e.g. 4 systems requires 6 interfaces, 5 systems = 10 interfaces, 6
systems = 15 interfaces, 10 systems require 45 interfaces .... and then
we move into mind blowing numbers !!
Whether you need to divide by two depends, of course, on how you define
an "interface" - but you are right in that bi-directionality is usually
assumed. Alas, the transformation of health data is rarely perfectly
symmetrical or commutative, so although the effort in writing those
interfaces involved is probably less than n(n-1), but is usually more
than n(n-1)/2
Tim C
Tim Churches wrote:
David Guest wrote:
Webservices does not seem that daunting a technology. My concern is
about standardising the minimum datasets and calls that they will
provide. Communication between disparate applications is much easier
with RPC/SOAP but you still don't want to write (n-1)! interfaces.
It's not as bad as you think, David! To get n information systems which
each use their own dataset definitions and semantics to talk to one
another, you only need write n(n-1) sets of interfaces, don't you?. For
n > 4, n(n-1) < (n-1)!
However, either way you are on a hiding to nothing. Bring on the
minimum/core dataset definitions (or I should say, let the argy-bargy
over what needs to be in the minimum/care dataset definitions commence!)!
Tim C
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