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(a) (i) What are the four basic symbols
used in data flow diagrams? [4]
(ii) Give an example of a data flow diagram that uses the four symbols
of
part (i). [4]
(a) (i) One mark should be awarded for correctly
illustrating each of the
following symbols:
- Entity
- Data flow
- Process
- Data store
Marks should not be awarded if a process is named and no
diagram is given. [4 marks]
(ii) Any suitable example should receive credit. Each symbol that
is
used correctly should receive one mark. [4 marks]
(b) (i) Differentiate between the terms
hard real-time process and soft real-time
process. [2]
(ii) Give one example of a hard real-time system and one example of
a soft
real-time system. [2]
(b) (i) Hard real-time processes are those
in which the application fails
completely if the process does not always meet the time constraint
(1 mark), whereas soft real-time processes are those in which the
system performance is only degraded if the time constraint is not
always met (1 mark).
Other correct answers should also receive credit. [2 marks]
(ii) An example of a hard real-time system is an aircraft flight control
system (1 mark), and an example of a soft real-time system is an
airline reservation system (1 mark).
Other correct answers should also receive credit. [2 marks]
(c) Describe the first step in developing
a structure chart from a data flow diagram. [3]
(c) The first step in developing a structure
chart from a data flow diagram
involves performing a transaction analysis (1 mark). The data flow
diagram is partitioned into units (called transactions) that, in turn,
can be
designed to derive the structure chart (1 mark). Transaction analysis
is
the technique of determining the transaction types of a system and
using
them as the units of design (1 mark). [3 marks]
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