%T High Cohesion and Low Coupling: the Office Mapping Factor
%A Řyvind Teig
%E Alistair A. McEwan, Steve Schneider, Wilson Ifill, Peter H. Welch
%B Communicating Process Architectures 2007
%X This case observation describes how an embedded industrial
software architecture was
&\[sh]8220;mapped&\[sh]8221; onto an office layout.
It describes a particular type of program architecture that
does this mapping rather well. The more a programmer knows
what to do, and so may withdraw to his office and do it, the
higher the cohesion or completeness. The less s/he has to
know about what is going on in other offices, the lower the
coupling or disturbance. The project, which made us aware of
this, was an embedded system built on the well\-known
process data\-flow architecture. All interprocess
communication that carried data was on synchronous, blocking
channels. In this programming paradigm, it is possible for a
process to refuse to &\[sh]8220;listen&\[sh]8221; on
a channel while it is busy doing other things. We think that
this in a way corresponds to closing the door to an office.
When another process needs to communicate with such a
process, it will simply be blocked (and descheduled). No
queuing is done. The process, or the programmer, need not
worry about holding up others. The net result seems to be
good isolation of work and easier implementation. The
isolation also enables faster pinpointing of where an error
may be and, hence, in fixing the error in one place only.
Even before the product was shipped, it was possible to keep
the system with close to zero known errors. The paradigm
described here has become a valuable tool in our toolbox.
However, when this paradigm is used, one must also pay
attention should complexity start to grow beyond
expectations, as it may be a sign of too high cohesion or
too little coupling.
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