Object Modeling THETOPPERSWAY.COM

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Object ModelingTHETOPPERSWAY.COM
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Object Modelling Technique(OMT)

• Building a model of an application domain and
  then adding implementation details to it.
• Following four stages-
• Analysis
• System Design
• Object Design
• Implementation.

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Three Models

• Object Model describes the static structure of
  objects in the system and their relationships.
• Dynamic Model describes the aspect of the
  system that change over time, i.e. interaction
  among objects.
• Functional Model describes data value
  transformation in the system.

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Object Model

• Describes the structure of objects in a system-
• - Identity
• - Relationship to other objects
• - Their attributes
• - And their operations.

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Dynamic Model

• Describes those aspects of the system concerned
  with time and sequencing of operations-
• Events that make change
• Sequence of events
• States that define context of events
• And organization of events and states.

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Functional Model

• Describes those aspects of the system concerned
  with transformation of values-
• Functions
• Mappings
• Constraints
• Functional dependencies
• Is represented with Data Flow Diagrams.

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Objects and Classes
Interpretation in the Real World Interpretation in the Model
Object An object is a thing that can be distinctly identified. An object has an identity, a state, and a behavior.
Class A class represents a set of objects with similar characteristics and behavior. This objects are called the instances of the class. A class characterizes the structure of states and behaviors that are shared by all instances.
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Objects

• Each of object has a unique identity.
• The state of an object is composed of a set of
  fields (data fields), or attributes.
• Each field has a name, a type, and a value.
• Behaviors are defined by methods.
• Each method has a name, a type, and a value.
• Each method may or may not return a value.
• Features are a combination of the state and the
  behavior of the object.

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Classes

• A class defines a template for creating or
  instantiating its instances or objects.
• A class is a description of a set of objects that
  share the same attributes, operations,
  relationships, and semantics.

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Example

• Class name Point class Point
• Fields x, y int x, y
• Method move public void move
• (int dx, int dy)
• // implementation

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UML Notation for Classes
ClassName The top compartment shows the class name.
field1 fieldn The middle compartment contains the declarations of the fields of the class.
method1 methodm The bottom compartment contains the declarations of the methods
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Object Model Notations

• Object classes are rectangles with the name at
  the top, attributes in the middle section and
  operations in the bottom section

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UML Notation for Object
ObjectName ClassName The top compartment shows the object name and its class.
field1 value1 fieldn valuen The bottom compartment contains a list of the fields and their values.
objectName -- objectName whose class is of no interest ClassName -- anonymous object of ClassName which can be identify only through its relationship with other object. objectName -- objectName whose class is of no interest ClassName -- anonymous object of ClassName which can be identify only through its relationship with other object.
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Examples
P1Point Point p1 new Point()
x 0 y 0 p1.x 0 P1.y 0
P1Point Point p1 new Point()
x 24 y 40 p1.x 24 P1.y 40
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Object Model Notations (Contd.)

• Relationships between object classes (known as
  associations) are shown as lines linking objects

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Example
Sample Data
L3
P2
P1
L1
L4
(Line) L1
Intersects
L2
(Point) P1
(Line) L2
Line
Point
Intersects
(Line) L3
name
name
2
(Point) P2
(Line) L4
Class Diagram
Instance Diagram
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Associations

• Connection between objects
• Solid line
• Direction optional
• Arrowhead depends on meaning
• Name (optional)
• Multiplicities (optional)
• Visibility (optional)

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Association

• Association represents binary relationship
  between classes

enroll

Student
Course
advisee


teach
1
1
Faculty
adviser
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Aggregation

• An aggregation model shows how classes that are
  collections are composed of other classes.
• Aggregation models are similar to the part-of
  relationship in data models.

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Aggregation and Compositon

• Aggregation is a special form of association
• Has-a or part-whole relationship
• Composition is a stronger form of aggregation

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Example
1
1
1



University
Department
College
Student
1
1
Chairman-of
Member-of
1
1..
Faculty
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Inheritance

• Define a relationship among classes and
  interfaces
• Inheritance model -- the is-a(n) relationship

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Example
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Multiple inheritance
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Generalization

• Models the concept of inheritance
• Subclasses inherit the attributes and operations
  of all their superclasses
• Objects of a subclass should be substitutable for
  objects of their superclasses
• Uses hollow triangle arrowhead on superclass

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Generalisation Example
Generalization
Specialization
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Abstract Classes

• Used to hold common operations and data
• Used in inheritance hierarchy
• Derived (child) classes provide implementations
• Documented with class name in italics
• Can also use abstract property

Shape abstract
move() erase() void abstract draw() void
abstract
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Constraints

• A restriction in the design
• Documented inside curly braces attached to any
  diagram element

Window
length
width
0.5lt(length/width)lt1.5
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Metadata

• Data about data.
• Data that describes other data.
• Metadata is defined as data providing information
  about one or more aspects of the data, such as
• Means of creation of the data
• Purpose of the data
• Time and date of creation
• Creator or author of data
• Location on a computer where the data was
  created.

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Candidate Keys

• Minimal set of attributes that uniquely
  identifies an object or link.
• It is denoted by braces C.K.
• Candidate key(Person, Company)

Person
Company
Works-for
name
name
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