Transcript OOAD - Sharif

Object Oriented
Analysis & Design
Outline
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Object Oriented Concepts and principals
Object Oriented Analysis
Object Oriented Design
OO Concepts and principals
Introduction
• We live in a world of objects
• Object-Oriented view is an abstraction that
models the world in ways that help us to better
understand and navigate it
• OO approach was first proposed in the late
1960s
• As time passes, object technologies are
replacing classical software development
approaches. Why?
• Object technologies lead to reuse, OO software
is easier to maintain, to adapt, and to scale.
OO Paradigm
• For many years, the term OO was used to
denote a software development approach that
used one of a number of OO programming
languages(e.g. Ada 95, C++, Eiffel, Smalltalk)
• Today, the OO paradigm encompasses a
complete view of software engineering
• Although any one of process models, could be
adapted for use with OO, the best choice would
be an evolutionary process model
The OO Process Model
OO Concepts
• Classes and class hierarchies
– Instances
– Inheritance
– Abstraction and hiding
• Objects
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Attributes
Methods
Encapsulation
Polymorphism
• Messages
Object
The object encapsulates
both data and the logical
procedures required to
manipulate the data method
method
#2
#1
data
method
#6
method
#5
Achieves “information hiding”
method
#4
Polymorphism
• It is a characteristic that greatly reduces the
effort required to extend an existing OO
system.
• Polymorphism enables a number of different
operations to have the same name.
• For example: drawing different type of
graphs( e.g. Line, Pie, Histogram )
• It decouples objects from one another making
each more independent.
• General class graph and one subclass for
each type.
Messages
sender object
attributes:
receiver object
attributes:
operations:
operations:
message:
[sender, return value(s)]
message: [receiver, operation, parameters]
Object Oriented Analysis
Modeling Dimensions
1.
2.
Identification/classification of entities.
General-to-specific and whole-to-part entity
relationships
The modeling
3. Other entity relationships
dimensions 8 and
9 are always
4. Description of attributes of entities
present with SA.
5. Large-scale model partitioning
6. States and transitions between states
7. Detailed specification for functions
8. Top-down decomposition
9. End-to-end processing sequences
10. Identification of exclusive services
11. Entity communications (via messages or events)
Conventional vs. OO Approaches
• Is OO analysis really different from the structured
analysis approach?
– A radical change over process oriented (SA).
– An incremental change over data oriented
methodologies (IE).
• Structured Analysis (SA):
– takes a distinct input-process-output view of
requirements.
– Data are considered separately from the processes
that transform the data.
– System behavior tends to play a secondary role.
– makes heavy use of functional decomposition.
The OOA Landscape
• Dozens of OOA method during the late 1980s and into the 1990s
are introduced.
• Each of them proposed:
– A process for the analysis of the product or system
– A set of diagrams that evolved out of the process.
– A notation that enabled the software engineer to create the analysis
model in a consistent manner.
• The most widely use were:
– The Booch method ( an evolutionary approach is maintained).
– The Rumbaugh method (Object modeling technique (OMT))
– The Jacobson method (OO Software Engineering (OOSE))
– The Coad and Yourdon method (One of the easiest)
– The Wirfs-Brock method (do not make clear distinction between
design and analysis tasks)
OOA & OOP
• OOA is based upon OOP: Classes and
members, Objects and attributes and so on
• To define them following tasks should be done:
– Basic user requirements should be communicated
between customer and software engineer
– Classes must be identified
– Class hierarchy should be specified
– Object to object relationship should be presented
– Object behavior should be modeled
– These task should be reapplied iteratively until model
is complete
Generic Steps for OOA
1. Elicit customer requirements for the system.
2. Identify scenarios for use-cases.
3. Select classes and objects using basic
requirements as a guide.
4. Identify attributes and operations for each
system object.
5. Define structures and hierarchies that organize
classes.
6. Build an object-behavior model.
7. Review the OO analysis model against usecases or scenarios.
A Unified Approach to OOA
• Grady Booch, James Rumbaugh and Ivar Jacobson
combine the best features into a unified method called:
Unified Modeling Language (UML)
• UML allows a software engineer to express and analysis
model using a modeling notation that is governed by a
set of Syntactic, Semantic, and Pragmatic rules.
– The syntax tells us how the symbols should look and how they
are combined. (Word in natural language)
– The semantics tells us what each symbols means and how it
should be interpreted. (Meaning of words in natural language)
– The pragmatic rules define the intentions of the symbols through
which the perpose of the model is achieved and become
understandable. (The rules for constructing sentences that are
clear and understandable in natural language)
UML and Analysis Views
• User model view. This view represents the system (product) from
the user’s (called “actors” in UML) perspective.
• Structural model view. Data and functionality is viewed from inside
the system. That is, static structure (classes, objects, and
relationships) is modeled.
• Behavioral model view. This part of the analysis model represents
the dynamic or behavioral aspects of the system.
• Implementation model view. The structural and behavioral aspects
of the system are represented as they are to be built.
• Environment model view. The structural and behavioral aspects of
the environment in which the system is to be implemented are
represented.
• UML analysis modeling focuses on the first two views of the system.
• UML design modeling addresses the other three views.
Domain Analysis
• OO Analysis can occur at many different levels of
abstraction:
– At the business or enterprise level
– At the business area level
– At an application level
• OOA at the middle level called Domain Analysis.
• Domain Analysis is performed to create a library of
reusable classes applicable to an entire category of
applications.
• Using a robust class library produces the system faster,
cheaper and more reliable.
• But where did such a library come from? By applying
domain analysis.
Domain Analysis Process
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The goal: to find or create those classes that are broadly applicable,
so that they may be reused.
It can be viewed as an umbrella activity for the software process.
The role of domain analyst is to design and build reusable
components that maybe used by many people working on similar but
not necessarily the same applications.
Key inputs and outputs for the domain analysis process:
class taxonomies
SOURCES OF
DOMAIN
KNOWLEDGE
technical literature
existing applications
customer surveys
expert advice
current/future requirements
DOMAIN
ANALYSIS
reuse standards
functional models
domain languages
DOMAIN
ANALYSIS
MODEL
Domain Analysis Activities (1)
• Define the domain to be investigated.
– Isolate the business area, system type, product category
– Extract both OO and non-OO items.
• OO-items such as: application and support (GUI, DB) classes,
Commercial off-the-shelf (COTS) component libraries and test
cases.
• Non-OO items such as: policies, procedures, plans, standards and
guidelines; parts of existing non-OO applications, metrics and
COTS non-OO software.
• Categorize the items extracted from the domain.
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Organize items into categories.
Define the general defining characteristics of the categories.
Propose a classification scheme for the categories.
Define naming conventions for each item.
Establish classification hierarchy when appropriate.
Domain Analysis Activities (2)
• Collect a representative sample of applications in the
domain.
– Ensure that the application has items that fit into categories.
• Analyze each application in the sample.
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Identify candidate reusable objects.
Indicate the reasons that the object has been identified for reuse.
Define adaptions to the object that may also be reusable.
Estimate the percentage of applications in the domain that make
reuse of the object.
– Identify the object by name and use configuration management
techniques to control them (chapter 9).
• Develop an analysis model for the objects.
– As a basis for design and construction of domain objects.
OOA- A Generic View
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define use cases
extract candidate classes
establish basic class relationships
define a class hierarchy
identify attributes for each class
specify methods that service the attributes
indicate how classes/objects are related
build a behavioral model
iterate on the first five steps
The OOA Process
• The OOA process begins with an understanding
of the manner in which the system will be used
by:
– People, if the system is human-interactive.
– Machines, if the system is involved in process control.
– Programs, if the system coordinates and controls
applications
• Once the scenario of usage has been defined,
the modeling of the software begins.
• A series of techniques may be used to gather
basic customer requirements.
Use Cases
Object Oriented Design
OOD
• OOD transforms the analysis model created using OOA
into a design model that serves as a blueprint for
software construction.
• OOD results in a design that achieves a number of
different levels of modularity.
• Subsystems: Major system components.
• Objects: Data and the operations.
• Four important software design concepts:
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Abstraction
Information Hiding
Functional Independence
Modularity
OOD
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The subsystem layer:
Representation of each of the
subsystems that enable the
software to achieve its customer
defined requirements.
The class and object layer: The
class hierarchies, (generalization)
and representation of objects.
The message layer: The design
details of communication of each
object with its collaborators.
(external and internal interfaces)
The responsibilities layer: Data
Structure and algorithmic design
for all attributes and operations.
OOA to OOD
OOA to OOD
Design Issues
• decomposability—the facility with which a design method helps the
designer to decompose a large problem into subproblems that are
easier to solve;
• composability—the degree to which a design method ensures that
program components (modules), once designed and built, can be
reused to create other systems;
• understandability—the ease with which a program component can
be understood without reference to other information or other
modules;
• continuity—the ability to make small changes in a program and have
these changes manifest themselves with corresponding changes in
just one or a very few modules;
• protection—a architectural characteristic that will reduce the
propagation of side affects if an error does occur in a given module.
Generic Components for OOD
• Problem domain component—the subsystems that are
responsible for implementing customer requirements
directly;
• Human interaction component —the subsystems that
implement the user interface (this included reusable GUI
subsystems);
• Task Management Component—the subsystems that are
responsible for controlling and coordinating concurrent
tasks that may be packaged within a subsystem or
among different subsystems;
• Data management component—the subsystem that is
responsible for the storage and retrieval of objects.
Process Flow for OOD
System Design Process
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Partition the analysis model into subsystems.
Identify concurrency that is dictated by the problem.
Allocate subsystems to processors and tasks.
Develop a design for the user interface.
Choose a basic strategy for implementing data
management.
Identify global resources and the control
mechanisms required to access them.
Design an appropriate control mechanism for the
system, including task management.
Consider how boundary conditions should be
handled.
Review and consider trade-offs.
System Design
Subsystem Example
Subsystem Design Criteria
• The subsystem should have a well-defined
interface through which all communication
with the rest of the system occurs.
• With the exception of a small number of
“communication classes,” the classes within
a subsystem should collaborate only with
other classes within the subsystem.
• The number of subsystems should be kept
small.
• A subsystem can be partitioned internally to
help reduce complexity.
Subsystem Collaboration Table
Object Design
• A protocol description establishes the interface
of an object by defining each message that the
object can receive and the related operation that
the object performs
• An implementation description shows
implementation details for each operation
implied by a message that is passed to an
object.
– information about the object's private part
– internal details about the data structures that describe
the object’s attributes
– procedural details that describe operations
Design Patterns
• add some example