SEG 4570 System Design and Implementation Tutorial 1

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SEG 4570System Design andImplementationTutoria
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Tutorial Content

• Procedural vs Object-Oriented
• Basic Concepts
• Design for a Library System
• I. Procedural Approach
• II. Object-Oriented Approach
• Procedural vs Object-Oriented

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Basic Concepts

• I. Procedural System Analysis Approach
• Examine a problem using input-processing-output
  (information flow) model and implement the model
  in the same way.
• It can be viewed as functional decomposition.
• II. Object-oriented Analysis (OOA)
• Examines requirements from the perspective of
  object-oriented concept such as classes, objects,
  attributes, operations and inheritance.
• It emphasizes the identification and
  classification of real-world entities into
  object-oriented components (object-oriented
  decomposition).

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Basic Concepts

• III. Coupling
• The degree of interaction between modules.
• 5 levels (high to low)
• Content coupling is when one module modifies or
  relies on the internal workings of another module
  (e.g. accessing local data of another module).
• Common coupling is when two modules share the
  same global data (e.g. a global variable)
• Control coupling is one module controlling the
  logic of another, by passing it information on
  what to do
• Stamp coupling is when modules share a composite
  data structure and use only a part of it (e.g.
  passing a whole record to a function which only
  needs one field of it).
• Data coupling is when modules share data through,
  for example, parameters.
• Modules should be loosely coupled.

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Designing a Library System

• Sample Problem
• Implements a simple library system which handles
  a information database of books.
• A database file consists of records of
  information about each book, including the books
  id, title, author, year and status is provided.
• The system is able to load the database file,
  allows user to perform keyword search of books
  through title and author, check out books and
  save the current information into the database.

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Design for a Library System Using Procedural
Approach

• 1. Problem identification
• Implement a library system
• Requirements
• I. Load database from database file.
• II. Search keyword through the title and
  author.
• III. Check out books.
• IV. Save current information to the database
  file.
• 2. Draw DFD to illustrate the data flow in the
  system (input-processing-output model)

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Design for a Library System Using Procedural
Approach

• A sample DFD

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Design for a Library System Using Procedural
Approach

• 3. Implement the model with Functions for each
  process
• I. Define a book structure II. Define a
  database structure
• 
  III. Define variables in main ( )

typedef struct char id char title
char author char year char status
Book
typedef struct int no_of_books char
db_name Book books50 Database
Database lib_db char cmd ...
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Design for a Library System Using Procedural
Approach

• IV. Define the following functions in separate
  modules

void loadDb(char db_file, Database ) void
saveDb(Database ) void search(char str_search,
Database ) void chkout(char str_id, Database
) int getCmd( ) void exeCmd(int
cmd_type) char getTitle(Book ) char
getAuthor(Book ) int getStatus(Book ) void
setStatus(Book )
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Design for a Library System Using Procedural
Approach

• A Library System Using Procedural Approach

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Design for a Library System Using Object-Oriented
Approach

• 1. Problem identification
• similar to Procedural Approach
• 2. Identifying and creating Objects
• I. List all nouns involved in the problem
• II. Group the nouns to form classes
• III. Design the communication between each
  class
• IV. Add methods to the classes
• V. Review the design to minimize no. of
  classes

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Design for a Library System Using OO Approach

• 3. Implement the model with Classes and Objects
• I. Book.h

class Book private String id String title
String author String year String status
public void setRecord(String record) void
setStatus( ) String getRecord( ) String
getTitle( ) String getAuthor( ) int
getStatus( )
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Design for a Library System Using OO Approach

• II. Database.h
• III. LibSys.h

class Database private int no_of_record
String db_name Book record50
public void loadDb(String db_file) void
saveDb( ) void search(String str_search) void
chkout(String str_id)
class LibSys private Database lib_sys
String cmd
public int getCmd( ) void exeCmd(int
cmd_no)
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Design for a Library System Using OO Approach

• A Library System Using OO Approach

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Procedural Approach vs OO

• 1. Modeling Power
• I. Modeling Power in Procedural Programming
• Restricted to functional models. Systems can only
  be modeled by information flow.
• Difficult to model systems with high complexity.
• II. Modeling Power in OOP
• Systems can be modeled by the interaction between
  objects which can better resemble the real world
  than traditional software can.
• This makes OOP easier to understand and the
  problem model more similar to the physical
  implementation model.

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Procedural Approach vs OO

• 2. Data Abstraction
• I. Abstraction in Procedural Programming
• Process Abstraction only
• Subprograms allow a calling program to specify
  that a process is to be done without spelling out
  how.
• e.g. ordinary functions, subprograms,
• Problems
• User-defined data do not have their own
  operations, any operation can access any data by
  parameter passing.
• Lead to high coupling between modules.

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Procedural Approach vs OO

• 2. Data Abstraction
• II. Data Abstraction in OOP
• Extend data abstraction to a higher level data
  type, which is called class.
• Data manipulation can only be done by operations
  specified in the definition of the data within a
  class.
• Classes can be viewed as as user-defined abstract
  data type where related data and their operations
  are hidden.
• It is also known as encapsulation.
• Advantages
• Modules becomes self-contained which greatly
  reduces the coupling between them.

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Procedural Approach vs OO

• 3. Modular Structure
• I. Modular Structure in Procedural Programming
• Modules are defined by functions which are more
  complicated.
• Modules are tightly coupled, changes to one part
  can easily lead to unforeseen behavioral changes
  in other parts.
• Relationships between modules cannot be easily
  discovered.
• Modules may need to be tested as a whole.

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Procedural Approach vs OO

• 3. Modular Structure
• II. Modular Structure in OOP
• Components of a OO system consist of
  self-contained objects, unexpected side effects
  in other modules occur less frequently after
  modifications are made.
• Relationship between modules can be easily seen
  from the header files.
• Individual modules can also be tested separately
  which makes system more reliable.

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Procedural Approach vs OO

• 4. Maintenance
• I. Maintenance in Procedural Programming
• Weak maintainability.
• Due to the high complexity and coupling between
  modules, it is difficult to understand the
  system.
• System cannot be easily modified to meet changes
  in requirement. i.e. not flexible.
• II. Maintenance in OOP
• As modules in OO system are easier to be modified
  and understood, maintenance can be done in a
  fraction of the time needed for traditional
  system.

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Procedural Approach vs OO

• 5. Reusability
• I. Reusability in Procedural Programming
• Modules with high coupling are difficult to
  reuse.
• II. Reusability in OOP
• Since objects are independent entities with their
  own data and operations, it is possible to reuse
  some objects in other applications.
• OOP supports inheritance and polymorphism which
  can greatly increase the module reusability.

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Conclusions

• 1. OOA has a better modeling power than
  structured approach through object-oriented
  decomposition.
• 2. OOP has a low mutual coherent between modules
  which make OO system more readable, maintainable,
  reliable, flexible and reusable.
• 3. Some OO features such as inheritance and
  polymorphism, which cannot be found in classical
  language, can greatly increase the quality of the
  OO system.