Course Name: High Level Programming Language
Year
: 2010
Modularity
Lecture 4
Learning Outcomes
At the end of this lecture, students are capable of:
• Understanding why modularity concept in programming is important.
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Outline Material
• Modularity I
–
–
–
–
–
Interface versus Implementation
Advantage using Interface
Decomposition of File
Abstract Data
Abstract Data and Module
• Modularity II
– Top-Down Programming and Bottom-Up Programming
– Cohesion
– Coupling
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Module:
Modularity I
• a unit from the whole organization of a
software system.
• groups together some functions, data, types,
etc.
Example: string functions from standard library Cstring
• hides detail of implementation from user’s
point of view (information hiding).
Ex.: local variable in C function, can not be
accessed by the caller function or main()
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Interface versus Implementation
Users and the module’s creator have a different
perspective about the module itself.
Interface: is an access point for users into a
module.
• it explains to users about how to use it.
• it makes a module easier to be used and
understood.
• it explains what services that the module
provides, not how it provides the services.
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Advantage of Using Interface
• Users can create their own program, before the
module is finished.
• Users programs and module program can be
compiled separately.
• Implementation of the module itself can be
changed, e.g. for fixing bugs, data structure, or for
a better algorithm; without changing or re-compiling
the users’ programs.
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Decomposition of File
Interface: header file (.h) contains declaration of
function, constant, variable, or users-defined types
that have public scope data behavior.
It also includes “comments” for users.
Implementation: source file (.c) that contains
definition of functions, along with local constants,
variable, and users-defined type for private scope
data behavior.
It also includes “comments” for the creator of that
particular module.
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Dekomposisi File
Users include header file, for functions that they
use, by using <#include the header files’s
name>. Pay attention, that this is enough to
compile the users programs.
Modules also include their header file, so that the c
compiler can check the consistency of the module
program, before it reaches the linking stage.
In the next slide, an example of interface is used for
a function service of linked-list.c
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Decomposition of File
Header File for linklist2.c
/* Sorted linked lists of chars */
/* Linked list nodes are of type node_t */
typedef struct element {
char contents;
struct element *next;
} node_t;
/* Inserts new node with contents `key', keeping
sorted.
`ptr_to_head’: address of pointer to head of list */
int insertNode(node_t **ptr_to_head, char key);
/* ... */
int deleteNode(node_t **ptr_to_head, char);
/* ... */
void traverse(node_t *head);
/* ... */
void deleteAllNodes(node_t **); 10
Data Abstraction
Abstract Data Type (ADT): A group of data and a group of
instruction that operates on that particular data, in which
the operation is independent from the module
implementation.
Example: stacks and lists.
Description of a Stack ADT:
Stack records data through a push and pop mechanisms.
And it has a LIFO (Last In First Out) behavior, which means
that input data will be in order, but output data will be in
reverse order.
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Abstraksi Data dan Modul
There is only one stack ADT, but there is another possibility to
implemented it. An particular implementation uses a particular
data structure and also has functions that manipulate that
particular data.
In C language, a person can implement stack ADT in link-list
or in array. The operations that are inside the stack ADT, are
functions that are declared inside the interface file (header file
.h).
However, details of how the operation works, does not
necessarily need to be known from the Users’ point of view.
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Modularity II
•Top-Down Programming and BottomUp Programming
•Cohesion
•Coupling
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Top-Down Programming and
Bottom-Up Programming
Important Rule #1
Desain with Top-Down,
but create with Bottom-Up
• Code and test the easiest component
first.
• Test every component, before using it to
create a more complex one.
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Coupling
Relation and dependency between
functions:
• Coupling Control:
– Happens when a function sends a signal
control to another function.
– Example: function call, return
• Coupling Data:
– Sending data between functions
– Example: function parameters, return
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values
Structure Diagram with label that shows data
coupling
Control Coupling
jam
nama
Example 1
Data Coupling
tanggal
undanganKePesta ( nama , tanggal ,
jam )
{
telepon ( nama )
ajakanKePesta (tanggal , jam )
inviteToParty
bye ( nama )
}
tanggal
jam
telepon
AjakanKePesta
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bye
Structure chart with labels showing data coupling
Example 2
telepon ( nama )
{
set nomerTelp sebagai hasil dari cariBukuAlmt (nama )
angkat telepon
tekan nomerTelp
katakan “Hi nama, Ini Budi”
}
ringUp
nomerTelp
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nama
Return value or data
that has been altered
using pointer
searchAddrBook
dll...
Important Points about Coupling
• Objective: To maximize independency
between module = to minimize coupling
• Use of Global Variables is not
recommended by data coupling’s
concept!
– It is recommended not to use global variable
in your program!
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Important Facts about Coupling
• Where do you use control coupling in coding?
– Function call: when a function is called, then
the control is given to that function
– Function return: when a coding inside a
function has been completed or done, then the
control is returned to the caller’s coding
• When do you use data coupling in coding?
– Data is sent to one function via parameter
– Data is returned from another function via
“return”
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– Data is modified using pointer
Cohesion
• Cohesion: refers to how close the
dependencies between lines of coding in one
particular function.
• Logical Cohesion Logic (weak)
– Ex.: Function Input / Output
• Function Cohesion (Strong)
– Function that results with one output or
activity.
• Purposes: function Cohesion
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Example of Cohesive
kontak ( perusahaan , pesan , mode )
{
if mode = fax
{
kirimFax ( perusahaan , pesan)
}
else if mode = email
{
kirimEmail ( perusahaan , pesan)
}
}
Cohesive
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Example of not Cohesive
kontak ( perusahaan , pesan , mode )
{
if mode = fax
{
kirimFax ( perusahaan , pesan)
}
else if mode = email
{
kirimEmail ( perusahaan , pesan)
}
}
cetakBukuAlamat ( )
Not Cohesive
}
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Cohesion
Important Rule #2
Modules inside structural
programming is tightly
cohesive, but having a loosely
coupling
• The amount of data coupling shows in
general the position of a module in a
programming hierarchy.
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Conclusion
• Modularity is an important concept in
creating a complex software
• Design top-down, but create it bottomup
• A good structure programming is one
that has behaviors as follow; very
cohesive with loosely coupling between
modules.
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Topic For Next Week
• Concurrent Versioning System
–
–
–
–
What is CVS – Concurrent Versioning System?
“Working Space” and “Repository Space”
Check-in and Check-out
Branch and Tag
• Assignment:
– CVS has been around from the beginning of software development. For
beginners, please read the following article, called “Tutorial-cvs.pdf”. <note:
you can download the article from the internet, i.e.:
wiki.wheder.net/images/0/0d/Tutorial-cvs.pdf or from binusmaya
download session in lecture 4.>
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Topic For Next Week
–Once you have read it, then install winCVS, and try to
implement from what you have read into the winCVS.
The only difference is that in the article it uses cvs
command line interface, while winCVS is an IDE CVS
for windows’ application.
–Make a report of your experiment with winCVS and it
will be discussed and presented
in the class.
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