1. Frank Tsui Software Engineering
CSE Colloquium
Frank Tsui
Software Engineering

2. 4 Topics Software Cohesion and Coupling Software Style and Metrics
Software Configuration Management
Software Process and Communications

3. 1. Software Cohesion and Coupling
Cohesion and Coupling are attributes of software
Conjectured and shown to be associated with:
software quality and
maintainability
Cohesion addresses the “relatedness” within a module or Class.
Coupling addresses the “relatedness” among modules or Classes

4. High Cohesion and Low Coupling
Research:
predictor
numerically
measurable
philosophical
& conceptual
If we consider a software system, the entities
in the system (e.g. for a Class, methods and
attributes form the entities of a Class) are evaluated
syntactically.
The number of attributes shared or the number of
methods evoked with in a class formulate the
basis for the cohesion metric of a Class.
The number of attributes “passed” or the number
of evocation of methods from one class to another
class formulate the basis for Class coupling metric

5. Example of a “simple” Class Cohesion Metric5
Instance variables in a class 1 2 3 4 M1 M2 M3
methods in a class
Let: ivj = instance variable j
N = Σ ivj
sivk = shared instance variable k
M = Σ sivk
then Class Cohesion = M/N
Many variants of this simple Class Cohesion metrics exist today.

6. 2. Software Style Research:
Is “Style” a software attribute ?
Style is still a philosophical and conceptual discussion
There is no clear concept or accepted definition
for “Style” of software.
It exists in other disciplines:
Music
Architecture
Clothes fashion
Etc.

7. Example from Kernighan and Plauger on identity matrix
for (int i = 1; i ≤ n ; i ++ )
{ { for ( int j = 1; j ≤ n; j++ )
M ( i,j ) = 0; }
M( i,i ) = 1 ;
for (int i = 1; i ≤ n ; i ++ )
{ for ( int j = 1; j ≤ n; j++ )
M ( i,j ) = ( i/j ) * ( j/I ); }

8. Consider two more sample code for answering the “sum of the first n integers”
Using Recursion
Sum ( n )
if ( n ==1 ) sum = 1;
else {
sum = n + sum ( n – 1 ); }
return sum ;
Using for Loop
Sum ( n )
sum = 0 ;
for ( int z = 1; z <= n ; z++ )
sum = sum + z;
What do you think about these two in terms of
- cohesion and coupling ?
- control structure?
- algorithm ?
- data ?
- and STYLE ?

9. Example from Pfleeger and Atlee on Tax Problem
Develop a software program that will compute
tax according to the following set of rules:
0 tax if income is zero .
10% tax for the first $10,000 or less
12% tax for next $10,000 above $10,000 OR ($10,001 to $20,000)
15% tax for next $10,000 above $20,000 OR ($20,001 to $30,000)
18% tax for next $10,000 above $30,000 OR ($30,001 to $40,000)
20% tax for above $40,000

10. tax = 0
if (taxable_income == 0) go to EXIT;
if (taxable_income > 10000) tax = tax ;
else {
tax = tax * taxable_income;
goto EXIT; }
if (taxable_income > 20000) tax = tax ;
else{
tax = tax * (taxable_income – 10000);
if (taxable_income > 30000) tax = tax +1500;
tax = tax * (taxable_income – 20000);
if (taxable_income ≤ 40000)
{ tax = tax * (taxable_income – 30000);
else
tax = tax * (taxable_income – 40000);
EXIT: ;
10% tax for the first $10,000 or less
12% tax for $10,001 to $20,000
15% tax for $20,001 to $30,000
18% tax for $30,001 to $39,999
20% tax for above $40,000

11. Code structure is different because the algorithm is
for (int i=2 ; level = 1; i <= 5; i++ )
{ If (taxable_income > bracket [ i ] )
level = level + 1;
else
{tax = base [ level ] + percent [ level ] * (taxable_income – bracket [level] ) ;
i = 6; }
Tax table showing the bracket, base, and the percent columns
bracket base percent
Code structure is different
because the algorithm is
dependent on a table of
Information, which may be
implemented with 3 arrays
e.g. float [ ] percent = {.10, .12, .15, .18, .20} and
assume array indexing start with 1

12. Computational “form” vs “role”
Consider someone asking you to add the first two integers:
You might say y = 1 + 2
Suppose we say ‘add the first 5 integers” ; you may still do the following
y =
Suppose we keep this up and ask you to add the first 50 integers!
y =
How about first 500 integers? ---- you may pause and try the following:
set iterator = 1
compute set sum = 0
sum <= sum + iterator
If iterator ≤ 500, compute iterator <= ( iterator + 1) and repeat the above statement;
otherwise, stop
The “role” did not change ---- at some point we changed the “form” ---

13. Inspirations of Previous “form” change ?
Rephrasing of 18th century English poet, William Blake’s stanza:
Can you see the world in a grain of sand?
Can you imagine heaven in a wild flower?
Can you grasp infinity in the palm of your hand?
Can you experience eternity in an hour?
Are these different forms of the same thing?
Expressing infinite computation requires a “form” change.
There may be many forms is style defined by form ?

14. Application to general “Iterator” pattern
The general iterator function (role) is to provide:
First ( )
Next ( )
Done ( )
Easy and similar to the previous example of adding integers
if the data type is integers.
- We also know the algorithms for data expressed with tree structure, by
specifying the traversal preference.
What about a non-structured set? { A, T, C, G, AAT, AATTCG } – do we
have to have a mapping to (some ordinal scale) ? If so, does that
mapping dictate the “form” of the iterator algorithm and thus the style?

15. This ADD function is parametric polymorphic in two ways:
Towards Polymorphism
ADD (max, data: dtype)
This ADD function is parametric polymorphic in two ways:
Max parameter gives us the capability of ADD to perform the sum of any arbitrary number of items, not just the first 25 items or first 600 items, etc.
Data parameter with potentially different data typing allows us to add different types of items.
Expanding the “role” in two dimensionalities, required us to
consider expanding the “form” differently ---- via parameters.

16. Related to “Polymorphism?”
Studying the various forms of design/coding leads us to some specific areas:
Varieties of polymorphism
Are the varieties of polymorphism a matter of:
“form” or
“role”
Would the number and type of “forms” and “roles” be a good starting point for the metric of “style?” for programs since all programs range from monomorphism to some degree of polymorphism.
The Component Based Design advocates will also find these concepts
closely related to “interfaces” and “services.”

17. 3. Software Configuration Management
Software Configuration Management is the discipline of controlling the evolution of software.
Has 2 main components:
Identifying & Defining the artifacts
that need to be controlled
2. Mechanism to control the artifacts

18. Configuration Management Research
Understanding and
Controlling “Relationships”
Among Artifacts
Focused on the “Control”
Mechanism
- versioning
- conflicts
- security
-access speed
-etc.
Moving towards

19. Intra & Inter Relationships
Requirements
Design
Code
Test Cases
general 3
general
general
general
general 1
general
general
general
general
French 2 4
French
French
French
French
Japanese
Japanese
Japanese
Japanese
Brazilian
Brazilian
Brazilian
Brazilian
Intra & Inter Relationships

20. Inter-Artifacts Relationship Matrix Example
Requirements
Elements
Design
Code Logic
UI Screens
DB tables
Initialization
data
Test cases X
Inter-Artifacts Relationship Matrix Example

21. 4. Software Process and Communications
It is conjectured that communications affects the success of software projects , especially with “Global Software Development”
Current
Research
How to
Relate ?
Software Project:
good morale
good product
meets schedule
meets cost
Communications:
types
structure
amount
Future
Research
Predict ?

22. Project Teams by Success and Amount of Communications
100 95
Success 90 85 80 75
1 k
2 k
3 k
4 k
5 k
6 k
7 k
8 k
Communications in person-minutes
Project Teams by Success and Amount of Communications

23. Distribution of Communications
39.7 40
% of
Total
Comm. 30
26.5
23.1 20
10.7 10
Req.
Des/code
Test
Proj. Mgmt
Distribution of Communications

24. Distribution of Communications by Groups45 40 35 B 30
9 teams
overall
% of
Total
Comm. 25 20 15 A 10 C 5
Req.
Des/code
Test
Proj. Mgmt
Distribution of Communications by Groups