Software Engineering for Students A Programming Approach

10.6 Discussion 135
■ teachable – people can be taught the method because it consists of well-defined steps
■ consistent – given a single program specification, two different people will come up
with the same program design.
■ simple and easy to use
■ produces designs that can be implemented in any programming language.
While these characteristics can be regarded as advantages, they can also be seen as a
challenge to the traditional skills associated with programming. It is also highly contentious
to say that data structure design is completely non-inspirational and rational.
In particular, some of the steps arguably require a good deal of insight and creativity,
for example, drawing the data structure diagram, identifying the elementary operations
and placing the operations on the program structure diagram.
Applicability
Data structure design is most applicable in applications where the structure of the
(input or output) data is very evident. Where there is no clear structure, the method
falls down.
For example, we can assess how useful this method is for designing computational
programs by considering an example. If we think about a program to calculate the
square root of a number, then the input has a very simple structure, and so has the output.
They are both merely single numbers. There is very little information upon which
to base a program structure and no guidance for devising some iterative algorithm that
calculates successively better and better approximations to the solution. Thus it is
unlikely that data structure design can be used to solve problems of this type.
The role of data structure design
Data structure design’s strong application area is serial file processing. Serial files are widely
used. For example, graphics files (e.g. JPEG and GIF formats), sound files (e.g. MIDI),
files sent to printers (e.g. PostScript format), Web pages using HTML, spreadsheet files
and word processor files. Gunter Born’s book (see Further Reading) lists hundreds of
(serial) file types that need the programmer’s attention. So, for example, if you needed to
write a program to convert a file in Microsoft format to an Apple Macintosh format, data
structure design would probably be of help. But perhaps the ultimate tribute to the
method is the use of an approach used in compiler writing called recursive descent. In
recursive descent the algorithm is designed so as to match the structure of the programming
language and thus the structure of the input data that is being analyzed.
The main advantages of data structure design are:
■ there is high “proximity” between the structure of the program and the structure of
the files. Hence a minor change to a file structure will lead only to a minor change
in the program
■ a series of well-defined steps leads from the specification to the design. Each stage
creates a well-defined product.