an automated ticket-issuing system used by passengers at a railway station
Chapter 10 Exercises
10.3 Giving reasons for your answers, suggest
an appropriate structural model for the
following systems:
- an automated ticket issuing system used
by passengers at a railway station;
The most appropriate architectural model
is a centralized model with a shared
repository of route and pricing information.
This means that changes are immediately
available to all machines. As little local
processing is necessary, there is no real
advantage in a client-server architecture.
The centralized system also allows global
information and route use to be collected
and processed.
- a computer-controlled video conferencing
system which allows video, audio, and
computer data to be visible to several
participants at the same time;
The most appropriate is a client-server model.
The reason for this is the need for a lot of
local processing to handle multimedia data.
- a robot floor cleaner which is intended
to clean relatively clear spaces such as
corridors. The cleaner must be able to
sense walls and other obstructions.
The most appropriate model is a repository
model where all subsystems place information
in the repository for other sub-systems to
use. In the case of AI systems as this would
be, a special kind of repository called a
blackboard is normally used.
10.5 Explain why a call-return model of control
is not usually suitable for real-time
systems which control some process.
The call return model assumes a sequence of
actions whereas real-time systems must respond
to events from different hardware interfaced to
the system. This normally means that the control
must be responsive rather than sequential.
10.6 Giving reasons for your answer, suggest an
appropriate control model for the following
systems:
- a batch processing system which takes
information about hours worked and pay
rates and prints salary slips and bank
credit transfer information;
Call return model of control. Each operation
involves identifying particular options then
calling subroutines to retrieve or compute
the required information. There are no
unexpected events to be processed
- a set of software tools which are produced
by different vendors but which must work
together;
Broadcast model of control is most appropriate.
Tools need not know which other tools are
available and this approach allows tools which
operate on different types of computers to work
together.
- a television controller which responds to
signals from a remote control unit.
Centralized (polling) control model. This is
the most appropriate approach as there is no
need for the very rapid response required from
interrupt driven systems.
