Lecture #11: Modularization
Reading: none
Handouts: Coupling and Cohesion

1. Greetings and felicitations
2. Interface
€	Where do you split things up?
€	look for parts of problems and places where higher-level stuff need not 
know about lower-level stuff ex.  database program for addresses
€	look for places where program is likely to change ex. machine-dependent 
code, organization-dependent code (use news, i/o buffers as examples) 
Then hide these using an interface which passes minimum, as few globals 
as possible
€	MAXIMUZE COHESION, MINIMIZE COUPLING (do handout)
€	ADVICE: KISS; "everything should be made as simple as possible, but no 
simpler"
3.	Modularity: how do you break things up?
… do "stack" as a module
… show breakdown: what are operations?
… what is data structure?
… 


Coupling and Cohesion
This handout presents the definitions of coupling and cohesion.


Levels of Coupling

best
5
.
Data 
Parameter lists.


4
.
Stamp 
³Named common,² that is, public variables shared only by 
those procedures that need to use them.


3
.
Control 
Flags passed between procedures to indicate what sections 
of code they should execute (what functions they should 
perform).


2
.
Common 
All procedures access all public variables.

worst
1
.
Content 
Procedures modify each others¹ internal variables or code.
(Assembly language).



Nowadays, a combination of Data Coupling and Stamp Coupling is considered the best 
solution to medium-sized programming problems: Stamp Coupling is used to create shared 
data structures for abstract data types, and Data Coupling for everything else.

In some rare instances, Stamp Coupling may be used in place of Data Coupling when 
efficiency problems make parameter passing too slow or large. This is, however, a rather 
unsatisfactory state of affairs.




Levels of Cohesion

best
6
.
Functional 
A procedure that accomplishes one clear function. 
Examples: a quicksort, a square root routine, a roman-
numeral evaluator.



Informational 
A group of procedures that work on the same data 
structure. Example: a module that implements an abstract 
data type.


5
.
Communicational 
A series of operations as in procedural cohesion ‹ but 
applied to the same data. Example: a procedure that reads 
the input stream and sorts it.


4
.
Procedural 
A series of operations that have something to do with each 
other, in terms of the overall problem being solved. 
Example: a procedure that reads the input stream, breaks it 
into roman numerals, and sorts the roman numerals.


3
.
Temporal 
A series of operations related in time (only). Common 
examples: a procedure that initializes all data structures 
used in a program, one that opens all files, etc.
  These operations typically have rather little to do with each 
other, but have strong connections with other parts of the 
program. (For example, a file must be opened here before it 
can be used in other parts of the program.)



2
.
Logical 
A set of related operations, where the caller chooses which 
to invoke. Example:

edit(op, string1, string2)

where op == 1 means replace, op == 2 means delete, 
and so forth. Historically this has sometimes been the poor 
man¹s form of Informational Cohesion but is no longer 
necessary.


worst
1
.
Coincidental 
No particular relation among operations. Common example: 
a large program arbitrarily hacked into ³modular² sections.





Lecture Notes	ECS 40 ­ FALL 1997	Page 1







Coupling and Cohesion	ECS 40 ­ FALL 1997	Page 4