chapter16 component design rpl

8/10/2019 Chapter16 component design RPL

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These courseware materials are to be used in conjunction with Software Engineering: A Practitioners Approach,5/e and areprovided with permission by R.S. Pressman & Associates, Inc., copyright 1996, 2001

Chapter 16Component-Level Design


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Component-Level Design

the closest design activity to codingthe approach:

review the design description for thecomponent

use stepwise refinement to develop algorithm

use structured programming to implementprocedural logic

use formal methods to prove logic


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Stepwise Refinement

open

walk to door;

reach for knob;

open door;

walk through;

close door.

repeat until door opens

turn knob clockwise;

if knob doesn't turn, then

take key out;

find correct key;

insert in lock;

endif

pull/push doormove out of way;

end repeat


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The Component-LevelDesign Model

represents the algorithm at a level of detailthat can be reviewed for quality

options:graphical (e.g. flowchart, box diagram)

pseudocode (e.g., PDL) ... choice of many

programming language

decision table

conduct walkthrough to assess quality


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Structured Programmingfor Procedural Design

uses a limited set of logical constructs:sequencecondi t ional if-then-else, select-casel oops do-while, repeat until

leads to more readable, testable code

important for achieving high quality,but not enough


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A Structured Procedural Design

a

x1

x2b

3x

4

5

c

d

ef

g

x

x

add a condition Z,if true, exit the program


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Program Design Language (PDL)

if-then-else

if condition xthen process a;

else process b;endif

PDL

easy to combine with source code

machine readable, no need for graphics input

graphics can be generated from PDL

enables declaration of data as well as procedure

easier to maintain


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Why Design Language?

can be a derivative of the HOL of choice

e.g., Ada PDL

machine readable and processable

can be embedded with source code,therefore easier to maintain

can be represented in great detail, ifdesigner and coder are different

easy to review

chapter16 component design rpl

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