Transcript CRC Cards & Use Cases

Chapter 22
Object-Oriented Systems
Analysis and Design and UML
Systems Analysis and Design
Kendall and Kendall
Fifth Edition
Major Topics
Object-oriented programming concepts
Object-oriented terminology
Five-layer model
CRC Cards
Unified Modeling Language
Use case and other UML diagrams
Relationships
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Object-Oriented Overview
Object-oriented techniques work well in
situations where complicated systems
are undergoing continuous
maintenance, adaptation, and design
There are two ways to model objectoriented systems
Coad and Yourdon methodology
The Unified Modeling Language
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Object-Oriented Programming
Six ideas characterize object-oriented
programming:
An object, which represents a real-world
thing or event
A class, or group of related objects
Messages, sent between objects
Encapsulation, only an object makes
changes through its own behavior
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Object-Oriented Programming
Six ideas characterize object-oriented
programming (continued):
Inheritance, a new class created from
another class
Polymorphism, meaning that a derived
class behavior may be different from the
base class
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Terminology
Class refers to a template for a group of
individual objects with common
attributes and common behavior
The difference between an Object and a
Class is that the class defines shared
attributes and behaviors of objects
An object is an instance or occurrence
of a class
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Terminology
Another name for property is attribute
Another name for method is operation
Interface means the behavior of a class
or component that is noticeable from
outside the class or component
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Encapsulation
Encapsulation changes the manner in
which data is updated by programs
because data can only be changed via
the services that encapsulate the data
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Inheritance
The two types of classes are involved in
any inheritance relationship are the
base class and the derived class
Multiple inheritance means there will be
multiple occurrences of the base type of
class in the inheritance relationship
Polymorphism only occurs where there
is inheritance
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Five-Layer Model
Object oriented analysis and design is
based on a five-layer model:
Class/object layer notes the classes and
objects
Structure layer captures various structures
of classes and objects, such as one-tomany relationships and inheritance
Attribute layer details the attributes of
classes
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Five-Layer Model
Five-layer model, continued
Service layer notes messages and object
behaviors
Subject layer divides the design into
implementation units or team assignments
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Five General Types of Objects
There are five general types of objects:
Tangible things
Roles
Incidents
Interactions
Specifications details
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Criteria to Determine Need for
a New Class of Objects
Criteria to determine whether a new
class of objects is justified
There is a need to remember the object
There is a need for certain behaviors of the
object
An object has multiple attributes
A class has more than one object
instantiation
Unless it is a base class
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Criteria to Determine Need for
a New Class of Objects
Criteria, continued
Attributes have a meaningful value for
each object in a class
Services behave the same for every object
in a class
Objects implement requirements that are
derived from the problem setting
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Criteria to Determine Need for
a New Class of Objects
Criteria, continued
Objects do not duplicate attributes and
services that could be derived from other
objects in the system
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Basic Types of Structures
There are two basic types of structures
that might be imposed on classes and
objects:
Generalization-Specialization structure
(Gen-Spec), which connect class-to-class
Whole-Part structure which are collections
of different objects that compose another
whole object
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Instance Connections
Instance connections are references
between objects such as associations or
relationships indicated by a single line
between objects using the same
cardinality notation as Whole-Part
structures
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Methods
Services (or methods or procedures)
must be analyzed. Activities are
Object state analysis, showing changes of
state
Service specification: creating, storing,
retrieving, connecting, accessing, and
deleting objects
Message specification, consisting of control
and data flow
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Major Components of ObjectOriented Design Activities
Object-oriented design activities are
grouped into four major components:
The
The
The
The
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problem domain component
human interface component
data management component
task management component
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Problem Domain Component
The problem domain component
consists of
Reuse design
Implementation structures
Language accommodation
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CRC Cards
Class, responsibilities, and collaborators
(CRC) cards are used to represent the
responsibilities of classes and the
interaction between the classes
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Creating CRC Cards
Analysts create CRC cards by
Finding all the nouns and verbs in a
problem statement
Create scenarios that are actually
walkthroughs of system functions
Identify and refine responsibilities into
smaller and smaller tasks, if possible
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Creating CRC Cards
Creating CRC cards, continued
The group determines how tasks are
fulfilled by objects or interacting with other
things
Responsibilities evolve into methods or
operations
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The Unified Modeling
Language (UML)
UML (Unified Modeling Language) is the
result of a collaboration of individual
object-oriented methods that has been
adopted as a standard for modeling
object-oriented systems
It differs from the Coad and Yourdon
OOA-OOD in the way that it breaks
down objects and their relationships
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The Unified Modeling
Language (UML)
UML has three categories:
Things, the objects
Relationships, the glue that holds things
together
Diagrams, categorized as either structure
or behavioral
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Use Case
A use case describes three things:
An actor (user) that initiates an event
An event that triggers a use case
The use case that performs the actions
triggered by the event
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Kinds of Use Cases
There are two kinds of use cases:
Primary, the standard flow of events within
a system that describe a standard system
behavior
Use case scenarios that describe variations
of the primary use case
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Steps for Creating a Use Case
Model
The steps required to create a use case
model are
Review the business specifications and
identify the actors within the problem
domain
Identify the high-level events and develop
the primary use cases that describe the
events and how actors initiate them
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Steps for Creating a Use Case
Model
Creating a use case model, continued
Review each primary use case to
determine possible variations of flow
through the use case
Develop the use case documents for all
primary use cases and all important use
case scenarios
Move to UML diagramming techniques to
complete the systems analysis and design
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Two General Groupings of
Things
There are two general groupings of
things in UML:
Structural things that define the conceptual
and physical structures of an O-O system
and are described by nouns
Behavioral things, the verbs of a UML
model that represent the behavior of the
system and the states of the system
before, during, and after the behaviors
occur
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Categories of Structural Things
There are seven categories of structural
things
The first five are conceptual or logical
The last two are physical in nature
Component
Node
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Categories of Structural Things
Seven categories of structural things:
Classes, which have properties or
attributes and methods or operations
Interfaces, the behavior of a class or
component of a system that is noticeable
from outside the class or component
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Categories of Structural Things
Seven categories, continued
Collaborations, which describe the
interactions of two or more things in a
system that perform a behavior that is
more than any one of the things can do
alone
Use cases, which describe a series of
actions that demonstrate a distinct
behavior of the system and its interactions
with the actors
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Categories of Structural Things
Seven categories, continued
Control or active classes
A control class can initiate and control an
independent flow of activity within the system
Components, which are a physical part of a
system that represents the services and
interfaces implemented by the elements
contained within that component, including
software code
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Categories of Structural Things
Seven categories, continued
Nodes, which represent a piece of
hardware on which your system executes
Components are physically deployed on nodes
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Behavioral Things
Behavioral things consist of
Interactions, or messages sent between a
set of objects within the system to perform
a specific task
State machine, a series of states that an
object goes through in response to actions
within the system
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Packages
Packages are groups of things
They can be physical subsystems
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Types of Relationships
There are two types of relationships
that hold things together:
Structural
Behavioral
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Types of Structural
Relationships
There are four types of structural
relationships:
Dependencies, where one thing affects
another thing that uses it
Aggregations, which show how the whole
object is composed of the sum of its parts
Associations that describe structural
connections between things
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Types of Structural
Relationships
Four types of structural relationships,
continued
Generalizations, which describe a
relationship between a general kind of
thing and a more specific kind of thing,
used for modeling class inheritance and
specialization
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Types of Active Behavioral
Relationships
There are four active behavioral
relationships:
Communicates is used to connect an actor
to a use case
Includes describes the situation where a
use case contains a behavior that is
common to more than one use case
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Types of Active Behavioral
Relationships
Types of active behavioral relationships,
continued
Extends describes the situation where one
use case possesses the behavior that
allows the new use case to handle a
variation or exception
Generalizes implies that one thing is more
typical than the other thing
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UML Structural Diagrams
UML structural diagrams include
Class diagrams used to model the static
structural design of a system
Object diagrams portray the state of class
instances and their relationships at a point
in time
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UML Structural Diagrams
UML structural diagrams, continued
Component diagrams show an overview of
the system architecture
A deployment diagram illustrates the
physical implementation of the system,
including the hardware
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Behavioral Diagrams
Behavioral diagrams describe the
interaction between people and a use
case
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Behavioral Diagrams
Behavioral Diagrams include
Use case diagrams, showing the actors and
the use cases
Sequence diagrams that depict a
succession of interactions between object
instances over time and they show the
processing described in use case scenarios
Activity diagrams show the flow of
activities within a process
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Behavioral Diagrams
Behavioral Diagrams, continued
Collaboration diagrams illustrate a
sequence of object interactions showing
the organization of the objects during the
interactions
State chart diagrams show the states of an
object and the events and conditions that
trigger a transition from one state to
another
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Steps Used in UML
The steps used in UML are
Define the use case model
Define the object model
Continue UML diagramming to model the
system during the systems analysis phase
Begin system design by refining UML
diagrams and using them to derive classes
and their properties and methods
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