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UML design from code. In certain cases, the whole program can be generated from a complete
UML description.
The UML story illustrates a marked trend in software evolution, from programmers writing
procedural code to programmers writing declarative program specifications, which are then
'understood' by a suitable generic processor and turned into procedural code.
Topic Declarative bit Processor Non-declarative
approach
Datahandling
using a
program
The file
containing the
data
The program
written to process
the data
Mapping The map The human brain
(able to find a
path from A to B,
for example)
Electronic
circuits
Spreadsheet
A computer-based
representation of
the circuit
(resistor R1
connected to
capacitor C3, etc)
The spreadsheet
itself (i.e. the
spreadsheet it is
when saved to
file: the .xls file).
Logic The logic
programming 'program' (facts
and rules) (see
Appendix A2.3)
Software tools
able to:
- simulate the
behaviour of the
circuit;
- prepare a circuit
layout for a
printed circuit
board;
- calculate the cost
of the circuit;
- calculate the
heat budget of the
circuit.
The spreadsheet
software, e.g.
Microsoft Excel.
The logic
programming
interpreter, e.g.
Prolog.
Write a program
which contains
the data in the
program itself.
Give
instructions
about how to get
from A to B.
Write a program
for each circuit
for each task.
E.g. one
program would
be needed to
simulate the
behaviour of a
specific circuit.
Write a program
to do the
calculations.
Difficult to
conceive doing
using
conventional
programming..
Advantages of a
declarative approach
Separate data from
program. Therefore
same data can be
analysed by different
programs; same
program can be used to
analyse different
datasets.
Map can be used to get
from many points to
many other points.
User constructs a
circuit in intuitive
terms (resistors,
capacitors, etc, and
their connections).
The one design can be
processed by multiple
tools.
Each tool can be used
for all possible circuits,
therefore huge savings
in effort.
Greater ease of use.
Support tools (e.g.
graphics; immediate
update of values).
Only feasible way of
tackling problems
involving logic-based
reasoning.
Table 5.2 Summary comparison of declarative and procedural software architectures