Object analysis and design

Object Oriented
Analysis & Design

Amandeep S. Patti
AP, Comp. Sc., PCTE

Object Oriented Analysis,
Modeling and Design
• OO is a SW development approach
• that is based on modeling objects from the
real world
• and then using the model to build a Language-
independent design.

2

Object-oriented approach is used by:

• OO Languages
• OO Databases
• OO Modeling
• OO Methodology

3

Object-oriented approach promotes:

• Better Understanding of requirements,
• Visualize a problem using graphical notations,
• Cleaner designs,
• And more maintainable systems.

4

Object oriented approach
is divided into:
• A set of object-oriented concepts
• A language-independent graphical notation
which can be used to analyze problem
requirements
• Design a solution to the problem,
• And then implement the solution in a
programming language or in database

5

Object-Orientation

• A way to organize software as a collection of
discrete objects
– that incorporate both data structure and
behavior.
• This contrasts with previous programming
approaches in which
– data structure and behavior are only loosely
connected.

6

Major aspects under
object-orientation:
• Identity
• Classification
• Inheritance
• Polymorphism

7

Identity

• Quantized data into
– discrete, distinguishable entities called objects.
• Objects can be
– concrete or conceptual
• Objects do have their own distinct identity
– even if their attributes are same.
• Objects do have unique handle.
– In comparison to real world where objects simply
exists, in programming languages each object has a
unique handle by which it is referenced.
8

Classification

• Objects with the same data structure
(attributes) and behavior (operations) are
grouped into a class.
• Class is an abstraction
– that describes important properties to an
application
– and ignores the rest.
• Each object is an instance of its class.

9

Inheritance

• Sharing or attributes and operations
– among classes based on hierarchical relationship.
• A superclass is general information
– that subclasses refine and elaborate.

10

Polymorphism

• Same operation may behave differently for
different classes.
• An operation is a procedure or transformation
– that an object performs or is subject to.
• An implementation of operation by a specific
class
– is called a method.

11

OO Development

• A way of thinking about SW based on
abstractions
– that exist in the real world as well as in the
program.
• Development refers to the SW Life Cycle
– analysis, design, and implementation.
– Integration, maintenance, and enhancement
• is automatically facilitated by a clean design in a
precise notation.

12

OO Development

• Modeling concepts, not implementation
• OO Methodology
• Three Models

13

Modeling concepts,
not implementation
• Front-end conceptual issues, rather than back-
end implementation details.
• OO Modeling as a conceptual process
– Independent of a programming language
• Serves as a medium
– for specifications, analysis, documentation,
interfacing and programming

14

OO Methodology

• OO methodology consists of
– Building a model of an application
– Then adding details to it during design.
• Stages
– System conception
– Analysis
– System design
– Class design
– Implementation
15

OO Themes
• Abstraction
• Encapsulation
• Combining Data and behavior
• Sharing
• Emphasis on the Essence of an Object
• Synergy

16

Modeling Concepts

• A Model is an abstraction of something for the
purpose of understanding it before building it.
• Modeling serves several purposes:
– Testing a physical entity before building it.
– Communication with customers.
– Visualization.
– Reduction of complexity by omitting nonessential
details.

17

Object Modeling Technique – OMT

• Different models are used to describe a
system from different viewpoints:
– Object Model / Class Model
– Dynamic Model / State Model
– Functional Model / Interaction Model
• Three models are separate parts to describe
system but are cross-linked.

18

Object Model / Class Model
• To describe static structure of the objects
• To describe relationship among various
objects
• Contains object/class diagrams
– Object/Class diagram is a graph diagram where
nodes are objects/classes and arcs are
relationships among objects/classes.

19

Dynamic Model / State Model

• To describes the aspects of an object that
change over time.
• Specifies and implements control.
• Contains state diagrams
– State diagram is a graph diagram where nodes are
states and arcs are transitions between states
caused by events.

20

Functional Model / Interaction Model

• Describes the data value transformations
within a system.
• Contains Data Flow diagrams
– Data flow diagram is a graph whose nodes are
processes/datastores and whose arcs are data
flows.

21

Object Modeling:

• Describes a model which capture the static
structure of a system
– by specifying the objects in the system and
relationship between them.
• Most important model
– as it emphasize building a system around objects
rather than around functionality.

22

Objects & Classes:
• Objects
– Corresponds to real world entities
• Classes
– Collection of the similar objects or entities.
• Each object is associated with the data of a
class which they are created.

23

Object Diagrams:
• Provide a format for graphical notation for
modeling the objects, classes and
relationships to on another.
• Types of object diagrams:
– Class Diagram
– Instance Diagram

24

Class Diagrams:

• Is a schema, pattern, or template for
describing many possible instances of data.
• describe the general case in modeling a
system.

25

Instance Diagrams:

• Describes object instances and show how a
particular set of objects relate to each other.
• Used mainly to show examples to help to
clarify a complex class diagram.

26

Attributes:
• Data value held by the objects in class.
• Each attribute has a value for each object
instance.
• Different object instances may have the same
or different values for a given attribute.
• Each attribute name is unique within a class.
• Should describe values not objects.
• Attributes are listed in the second part of the
class box. 27

Operations and Methods:

• An operation is a function or transformation
– That may be applied to or by objects in class.
• All objects in a class share same operations.
• Same operation may apply to many different
classes and is called polymorphic.
• A method is the implementation of an
operation for a class.
• Operations listed in the lower part of the class
box. 28

Links & Associations:

• A Link is a physical or conceptual connection
between object instances.
• An association describes a group of links
– with common structure and common semantics.
• Association and links often appear as verbs in
the problem statements.
• An association describes a set of potential
links in the same way that a class describes a
set of potential objects.
29

Degree of association:

• Describes the number of classes connected by
association:
– Unary association or reflexive association
– Binary association
– Ternary association
– Quaternary association
– Higher order association

30

Multiplicity:
• Denotes the cardinality of the association.
• It shows how many instances of one class may
relate to a single instance of an associated
class.
– One-to-one
– One-to-many
– Many-to-many

31

Role Names:
• Uniquely identify one end of an association.
• Roles often appear as nouns in the problem
statement.

32

Ordering:
• Objects on the “many” side of an association
have no explicit order, and is regarded as a
set.

33

Qualification:

• Special attribute that reduces the effective
multiplicity of an association.
• A qualified association relates two object
classes and a qualifier.

34

Aggregation:
• Is an extension of association
• Is the “part-whole” or “a-part-of” relationship
– In which objects representing the components of
something are associated with an object
representing the entire assembly.

35

Generalization:
• Is the relationship between a class and one or
more refined versions of it.
• Class being refined is called the superclass and
each refined version is called a subclass.
• Is a bottom-up process.
• Attributes and operations common to a group
of subclasses
– are attached to the superclass
– and shared by each subclass
36

Notation for Generalization:

• The notation for generalization is a triangle
– Connecting a superclass to its subclasses.
– The superclass is connected by a line to the apex
or the triangle.
– The subclasses are connected by lines to a
horizontal bar attached to the base of the triangle
• The dangling subclass ellipsis is used to
indicate that there are additional subclasses
that are not shown.
37

Use of Generalization:

• Useful for conceptual modeling as well as for
implementation
• Facilitates modeling
– by structuring classes
– capturing what is similar and what is different
about classes.

38

Specialization:
• Is a mechanism for refining the definition or
members of class.
• Is a top-down process.

39

Inheritance:
• Is a mechanism of sharing attributes and
operations among classes.
• May be of type:
– Single Inheritance
– Multiple Inheritance

40

Overriding Features:
• A Subclass may override a superclass feature
by defining a feature with the same name.
• The overriding feature refines and replaces
the overridden feature.

41

Association and Aggregation
Comparison :
• Both concepts provide the relationship among
the classes.
• Aggregation is not an independent concept
– but a special form of association.
– exists after the existing of association.
• Associations are bidirectional but
aggregations are antisymmetric.

42

Aggregation and Generalization
Comparison :
• Aggregation provides the relationship
between classes, while generalization is a
process to combine the common behavior and
attributers in a single or more classes.

43

Generalization and Specialization
Comparison :
• Two different viewpoints of the same
relationship
– Viewed from subclasses to superclass is called
generalization
– Viewed from superclass to subclasses is called
specialization
• Both are opposite to each other
– Generalization uses bottom-up approach
– Specialization uses top-down approach.
44

Dynamic Modeling:

• Describes changes to the objects and their
relationships over time.
• Represents the temporal, behavioral, control
aspects of a system.
• Major concepts are
– Events
• represent external stimuli and point of time
– States
• represent values of objects and interval of time
45

Event:
• Happens at a point in time
• One event may be casually related
– logically precede or follow another
• or the two events may be casually unrelated
– Concurrent
• Every event is a unique occurrence
– but can be grouped into event classes
– where event class indicate common structure and
behavior.
46

Event:
• An event is a one-way transmission of
information from one object to another.
– An object sending an event may expect reply
– but that reply is a separate event under the
control of the second object.
• Some classes of events may be simply signals
– that something has occurred
• Some classes of events may convey data
values called attributes of that event.
47

Scenario:
• Is a sequence of events
– that occurs during one particular execution of a
system
• Scope of a scenario can vary
– May include all events in the system
– Or may include only those events impinging on or
generated by certain objects in the system
• Next step after writing a scenario is to identify
the sender and receiver objects of each event.
48

Event Trace Diagram:
• The sequence of events and the objects
exchanging events can both be shown in an
augmented scenario called an even trace
diagram.
• Event diagrams shows
– Each object as a vertical line
– Each event as a horizontal arrow from the sender
object to the receiver object

49

Event Trace Diagram:

• Time increases from top-to-bottom
• Only the sequences of events are shown
– Not their exact timing.

50

State:

• Is an abstraction of the attribute values and
links of an objects.
• corresponds to the interval between two
events received by an object.
• specifies the response of the object to input
events.

51

State Diagram:

• Is used to relate events and states.
• On the occurrence of an event, next state
depends
– on the current state
– as well as on the event
• A state diagram is a graph where
– nodes are states and are drawn as rounded box
– and directed arcs are transitions and are drawn as
arrow and labeled by event names
52

Functional Modeling:

• Specifies the results of a computation without
specifying how or when they are computed.
• Shows which values depend on which other
values and the functions that relate them.

53

Relation with Object
and Dynamic Models:
• The functional modal specifies
– the meaning of the operations in the object model
– and the actions in the dynamic model,
– as well as any constraints in the object model.
• The Functional Model specifies what happens
• The Dynamic Model shows when it happens
• The Object Model specifies what it happens to

54

Data Flow Diagrams:

• Shows the functional relationships of the
values computed by a system
– Including input values, output values, and internal
data stores
• DFD is a graph showing the flow of data values
– from their sources
– through processes that transforms them
– to their destinations.

55

Data Flow Diagram Contains:

• Processes
– that transform data
• Data Flows
– that move data
• Actor objects
– that produce or consume data
• Data store objects
– that store data passively
56

Processes:

• A process transforms data values.
• A process is drawn as an ellipse containing a
description of the transformation.
• Each process has a fixed number of input and
output data arrows.
• The lowest-level processes are pure functions.
• The high-level processes may be whole DFD.
• Processes are implemented as methods.
57

Data Flows:

• A data flow connects the output of an object
or process to the input of another object or
process.
• A data flow is drawn as an arrow between the
producer and the consumer of the data value.

58

Data Flows:

• A fork with several arrows emerging from it
may be used to represent
– Flow of same value to several places
– Splitting an aggregate data value into its
components, each of which goes to a different
place.

59

Actors:

• An actor is an active object that drives the
data flow graph by producing or consuming
values.
• Actors are attached to the inputs and outputs
of a data flow graph.
• Also known as terminators.
• An actor is drawn as a rectangle.

60

Data stores:

• A data store is a passive object that stores
data for later access.
• A data store allows values to be accessed in a
different order than they are generated.
• It is drawn as a pair of parallel lines containing
the name of the store.

61

Actors vs. Data stores:

• Both actors and data stores are objects.
• They are distinguished because of their
behavior and usages.
• Data store might be implemented as a file and
an actor as an external device.

62

Context Diagram:

• It is the first DFD for every system.
• It shows the overall system processing as just
one process and shows the data flows to and
from external entities called actors.

63

Section A:

• Abstract Data Types: Model of Real World,
Autonomy, Generation of correct
Applications, Reusability Classes, Instance
Values, Methods and Messages, Creating and
destroying Objects, Constraints on object and
Instance Variables, Pre and Post conditions of
Methods.

64

Model of Real World:

• Real world objects are not like variables and
functions
• They have attributes and behaviour.
• All the information is packaged under one
name and can be reused as one specification
or programming component.

65

Autonomy:

• Means independence, freedom from the hold
of previous procedural programming
approaches.
– Redundant code is eliminated and the existing
classes can be extended through inheritance.
– Bugs in the program by usage of same member’s
names can be avoided due to encapsulation.
– Multiple instances may exist without interference.

66

Generation of Correct
Applications:
• OOAD simplifies the problem as it related the
problem with real world.
• As abstraction in generated first that
facilitates creating classes, thus chances of
errors are avoided.
• Reusability of existing classes further helps in
reducing errors

67

Instance Values:

• By instance we mean an object and by
instantiating a class, we make the objects of a
class.
• Every instance got features from the class it is
instantiated from but represent a completely
different object.
• Values that represent an object identity and
features form the instance values.

70

Methods and Messages:

• An object encapsulates data and algorithms
called methods that process that data.
• Messages are the means by which the objects
interact.
• A message stimulates some behaviour to
occur in the receiving objet.

71

Creating and Destroying Objects:

• Creation of objects is basically making copies
of the class members.
• Memory allocation is done.
• Creation of objects also includes its
initialization.
• Release the memory.

72

Constraints on Objects and
instance variables

73

Pre and Post Conditions or
Methods

74

Section A:

• Inheritance: Subsets as Subtypes, Sub typing of Structured
Types Contrasting in inheritance with subtyping, Implicit
Subtyping verses Explicit inheritance, Subtyping and dynamic
binding class inheritance. Redefining Instance variables,
Hiding Instance Variables inheriting methods, Method
Overriding, Invoking Superclass method, Constrained
Overriding, Inheriting the Interface, Excluding Super class
Methods metaclasses, Explicit Support, Implicit of hidden
Metaclasses, Object Oriented Languages without
Metaclasses, Prototype Systems and Delegation, Multiple
inheritance.

75

Inheritance:

• Deriving something more specific from a
generalized existing thing.
• Common characteristics are collected into one
specific class and other classes inherit that
class.
• Core idea for reuse
• Avoid redundancy
• Leading to smaller models
76

Inheritance with subtyping:

• Class is regarded as an implementation of a
type
– which defines certain behaviour.
• A subclass represents a subtype to a class.
• Ancestor represents a subset of the behaviour
common to all the descendants.
• Subtyping normally occurs if the inheritance
performs only an extension rather than
overriding.
77

Instance variables:

• A variable associated with a specific instance
is called an instance variable.
• Instance variable store instance’s state.
• Encapsulation ensures that only one way to
affect an object’s state, and that is though its
operations.

78

Hiding instance variables:

• Local variable having the same name as
instance variable can hide the instance
variable.

79

Overriding:

• Redefine some behaviour while inheriting
from ancestor.
• With overriding, inheritance would not remain
transitive.

80

Invoking super class method:

• To use characteristics from more than one
class.
• Controversial in the object-oriented
community.
• Reduces understanding of a class hierarchy.
• Having same name in more than one super
class creates problem

81

System Design:

• It is the first design stage
– in which the basic approach for solving the
problem is selected.
• System architecture is the overall organization
of the system into components called
subsystems.

82

Key issues in System Design:

• Organize the system into subsystems.
• Identify concurrency inherent in the problem.
• Allocate subsystems to processors and tasks.
• Choose an approach for management of data stores.
• Handle access to global resources.
• Choose the implementation of control in software.
• Handle Boundary Conditions.
• Set trade-off Priorities.

83

Organize the system into
subsystems:
• A subsystem is usually identified by the service it
provides.
• It is a package of
– interrelated classes, associations, operations, events and
constraints.
– Are reasonably well-defined.
– Interfaced with other subsystems.
• The lowest level subsystems are called modules.

84

subsystems:
• Relationship between two subsystems can be
– Client-supplier relationship
– Peer-to-peer relationship

85

subsystems:
• Client-supplier relationship
– Client calls on the supplier, which perform some service
and replies with a result.
– Client must know the interface of the supplier, but the
supplier does not have to know the interface

86

subsystems:
• Peer-to-Peer relationship
– Each of the subsystems may call on the others.
– Subsystems must know each other's interface
• Which makes it more complicated.
– Peer-to-Peer Relationship
• Each of the subsystems may call on the others.
• Subsystems must know each other's interface.

87

subsystems:
• Decomposition of system into subsystems:
– Layered Architecture
• Subsystem knows about the layers below it, but has no knowledge
of the upper layers
• Client supplier relationship exists between lower and upper layers
• Each layer is implemented in terms of classes and operations of
lower layers.
• It may be Closed Architecture or Open Architecture
– Partitions
• Vertically divide a system into several independent or weakly
coupled sybsystems.

88

Identifying concurrency:

• The objects are said to be concurrent
– if they can receive events at the same time
– without interaction.
• Identify which objects must be active con-currently
Identify which objects have activity that is mutually
exclusive.

89

Allocate subsystems to
processors and tasks:
• Each concurrent subsystem must be allocated to a
hardware unit
– either a general purpose processor
– or a specialized functional unit
• System designer must consider following aspects:
– Estimate performance needs and the resources needed to
satisfy them.
– Choose h/w or s/w implementation for subsystem.

90

Choose an approach for
management of data stores:
• Data store may combine
– Data structure
– Databases
– Data files

91

Handle access to
global resources.:
• System designer must Identify global resources and
determine mechanism for controlling access to them
• Physical object
– Can control itself by establishing a protocol for obtaining
access within a concurrent system.
• Logical object (such as object ID)
– There is danger of conflicting access in a shared
environment.
• Global resource must be owned and locking
mechanism should be implemented.
92

Choose the implementation of
control in software:
• External Control
• Internal Control

93

Handle Boundary Conditions:

• Initialization
– System must initial with all required things.
• Termination
– System must contain the termination statements
– Abnormal terminations must be avoided.
• Failure
– Abnormal termination is called failure
– May arise due to user errors, exhaustion of system
resources, external breakdown.

94

Set trade-off Priorities:

• Based on relative importance of the various criteria

95

Common Architectural
Frameworks:
• Functional Transformation System
– Batch Computation system
– Continuous Transformation system
• Time dependent system
– Interactive Interface
– Dynamic simulation
• Database system
– Transaction manager

96

Object analysis and design

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