OBJECT MODELING Flashcards
What is object-oriented Analysis
Object-oriented (O-O) analysis describes an information system by identifying things called objects
O-O analysis sees a system from the viewpoint of the objects themselves as they function and interact
For example, when a patient makes an appointment to see a doctor, the patient is an object, the doctor is an object, and the appointment itself is an object
What is the end product of O-O analysis
The end product of O-O analysis is an object model, which represents the information system in terms of objects and O-O concepts
UML will be used to develop object models
Describe an object and how it differs from DFDs
An object represents a person, a place, an event, or a transaction that is significant to the information system
DFDs are created to treat data and processes separately. An object, however, includes data and the
processes that affect the data
Illustrate how UML represents Objects
*See notes
Describe Attributes
An object has certain attributes, which are characteristics that describe the object
Some objects might have a few attributes; others might have dozens
Objects can inherit, or acquire, certain attributes
from other objects
What is a state
Objects can have a specific attribute called a state
The state of an object is an adjective that describes the object’s current status
For example, depending on the state, a bank account can be active, inactive, closed, or frozen
Describe Methods
Methods are tasks or functions that the object performs when it receives a message, or command, to do so
For example, a car performs a method called OPERATE WIPERS when it is sent a message with the wiper control
A method defines specific tasks that an object can perform
Methods resemble verbs since they describe what and how an object do
Describe object messages
A message is a command that tells an object to perform a certain method
The same message to two different objects can produce different results
The concept that a message gives different meanings to different objects is polymorphism
*See notes for example
Explain the black box concept in object messages and its advantages
An object can be viewed as a black box, because a message to the object triggers changes within the object without specifying how the changes must be carried out
The black box concept is an example of encapsulation, which means that all data and methods are self-contained
A black box does not want or need outside interference, hence modularity is well accomplished
Which programming languages are used to implement O-O designs
Research
What is the major advantage of O-O designs
systems analysts can save time and avoid errors by using objects, and
programmers can translate the designs into code, then
work with reusable program modules that have been tested and verified
Describe a class and an instance
An object belongs to a group or category called a class
-For example, Ford belong to a class called CAR
An instance is a specific member of a class
Many instances of the CAR class may be
observed:
-The TRUCK class, the MINIVAN class, and the
SPORT UTlLITY VEHICLE class
Relate objects and classes
All objects within a class share common attributes and methods, so a class is a blueprint or template for all the objects within the class
Objects within a class can be grouped into subclasses, which are more specific categories within a class
For example, TRUCK objects represent a subclass
within the VEHICLE class, along with other subclasses called CAR, MINIVAN, and SCHOOL BUS
Describe relationships among objects and their importance
Relationships describe what objects need to
know about each other, how objects respond to changes in other objects, and the effects of membership in classes, superclasses, and subclasses
Relationships enable objects to communicate and interact as they perform business functions and transactions required by the system
Some relationships are stronger than others
What is the strongest relationship?
The strongest relationship is called inheritance
Inheritance enables an object, called a child, to derive one or more of its attributes from another object called a parent
Describe the object relationship diagram and its importance
The model shows the objects and how they interact
to perform various function
That model is used as a guide to continue to develop additional diagrams and documentation and to provide an overview of the system
Describe Use Case Modelling
A use case represents the steps in a specific business process
An external entity/an actor initiates a use case by requesting the system to perform a process
Describe and illustrate the symbols used in a use case diagram
The UML symbol for a use case is an oval with a label that describes the action or event
-The actor is shown as a stick figure with a label that
identifies the actor’s role
-The line from the actor to the use case is called an association because it links a particular actor to a use case
*See notes for illustrations
Describe and illustrate how a use case can interact with other use cases
When the outcome of one use case is incorporated
by another use case, we say that the second case uses the first case
UML indicates the relationship with an arrow that points at the use case being used
*See notes for illustrations
How does start one create a use case
To create use cases, start by reviewing the information that was gathered during the requirements engineering phase
The objective is to identify the actors and the processes they initiate
For each use case, develop a use case description in the form of a table
What is contained in a use case description document
the name of the use case, the actor, a description of the use case, a step-by-step list of the tasks and actions required for successful completion, a description of alternative courses of action, preconditions, postconditions, and assumptions
*See notes for example
Describe the use case diagram
A use case diagram is a visual summary of several related use cases within a system or subsystem
Describe the use case diagram
A use case diagram is a visual summary of several related use cases within a system or subsystem
Describe how a use case diagram is drawn
When a use case diagram is created, the first step is to identify the system boundary, which is represented by a rectangle
The system boundary shows what is included in the
system (inside the rectangle) and what is not included in
the system (outside the rectangle)
After the system boundary is identified, use cases
are placed on the diagram, the actors are added and the relationships are shown
Describe and illustrate class diagrams
A class diagram shows the object classes and relationships involved in a use case
Class diagrams evolve into code modules, data objects, and other system components
*See notes for illustration
Describe and illustrate cardinality in class diagrams
The class diagram includes a concept called cardinality, which describes how instances of one class relate to instances of another class
For example, an employee might have earned no vocation days or one vacation day or many vacation days
*See notes for illustration
Describe the sequence diagram
A sequence diagram is a dynamic model of a use case, showing the interaction among classes during a specified time period
A sequence diagram graphically documents the use case by showing the classes, the messages, and the timing of the messages
Describe and illustrate the symbols used in sequence diagrams
Sequence diagrams include symbols that represent classes, lifelines, messages, and focuses
- A class is identified by a rectangle with the name inside. Classes send or receive messages
- A lifeline is identified by a dashed line. The lifeline represents the time the object above it is able to interact with the other objects in the use case. An X marks the end of the lifeline
- A message is identified by a line showing direction that runs between two objects
- A focus is identified by a narrow vertical shape that covers the lifeline. The focus indicates when an object
sends or receives a message
Describe the state transition diagram
A state transition diagram shows how an object changes from one state to another, depending on events that affect the object
All possible states must be documented in the state
transition diagram
Describe and illustrate the symbols in a state transition diagram
The states appear as rounded rectangles with the state names inside
The small circle to the left is the initial state or the point where the object first interacts with the system
Reading from left to right, the lines show direction and describe the action or event that causes a transition from one state to another
The circle at the right with a hollow border is the final state
*See notes for illustration
Describe the activity diagram
An activity diagram resembles a horizontal flowchart
that shows the actions and events as they occur
Activity diagrams show the order in which the actions take place and identify the outcome
illustrate the symbols in an activity diagram
*see notes
