3.Identifying Relation

8/8/2019 3.Identifying Relation

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Identifying Object Relationships,

Attributes and Methods


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Identifying Relationships

There are three types of relationships that may exists in

between any two objects

Association

Super-Sub Structure

Aggregation (A special case of association)


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Association

Represents a physical or conceptual connection betweentwo objects

Identifying Associations

Analyzing the interactions between classes The following questions are answered for identification of

associations

Is the class capable of fulfilling the required task by itself?

If not, what does it need?

From what other class can it acquire what it needs?


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Guidelines for identifying association

A dependency between two or more classes may be anassociation. Association often corresponds to a verb or

prepositional phrase such as part-of, next-to, works-for,

etc.,

A reference from one class to another is an association.

Some associations are implicit or taken from general

knowledge

Choose the association names carefully. Add role

name where appropriate.


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Common association Patterns

Location Association -

next-to, part-of, contained-in, etc.,

Communication Association -

talk-to, order-to, etc.,

Cheese Soup

Part of

Customer Operator Order-to


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Super-Sub relationships

Represents the inheritance relationship between related

classes

This is also called as generalization hierarchy.

The top level class more general called as base, superclass or ancestor

The bottom level class more specific called as derived,

sub class or successor


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Guidelines for identifying super-sub relation

Top-down

Look for the noun phrases composed of various adjectives in a class

name. E.g.., A tall man and a short man

Bottom-up

Look for the classes with similar attributes or methods. The commons

are grouped into super class

Reusability

Move the attributes and behaviors to the top-level of the hierarchy.

Dont create specialized class in the top-level.


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Multiple Inheritance

Avoid using multiple inheritance. Since they are very

complicated in implementation point of view. Use only the

class that is more appropriate as super class and define the

other classs attributes here also.


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Aggregation

Represents the situation where a class consists of several

component classes

Properties of Aggregation

Transitivity

If A is a part-of B and B is a part-of C. Then A is a

part-of C.

Antisymmetry

If A is a part-of B. Then B is Not a part-of A.


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Identifying Aggregation

The following questions are answered for identification of

aggregation

Does the part class belong to the problem domain?

Is the part class within the systems responsibilities?

Does the part class capture more than a single value? If single

value then set it as an attribute.

Does it provide a useful abstraction in dealing with problem

domain?


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Aggregation Relationship Patterns

Assembly -

An assembly is constructed from its parts.

E.g.., Coffee is assembly of Coffee powder, water

Container -

The container contains, not constructed from the parts.

E.g.., House contains furniture and other appliances.

Collection member -

Collection of conceptual or physical parts.

E.g.., Cricket team is a collection of players


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Identifying Attributes

The attributes are identified from scenario testing.

Hence by analyzing the use-cases, sequence, collaboration,state chart, activity diagrams, the classes responsibilities

are identified.


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Guidelines for identifying attributes

Attributes are usually corresponds to nouns, phrases,

adjectives and adverbs.

Keep the class simple. State only enough attributes.

Attributes are less defined in the problem statement. It is

obtained by general knowledge.

Omit derived attributes

Dont waste much time in finding attributes. This can bedone in successive iterations.


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Identifying Methods and Messages

Methods are the services provided by the objects

They are responsible to manage the value of the attributes.


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Identifying methods by analyzing UML diagrams

The sequence diagram says about the events that occur

between two objects.

This event is considered to be an action that transmits

information between two objects

These actions are the methods that the object should

perform.

For each class the methods are defined by analyzing the

sequence diagram of all the related use-cases


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For E.g.., for account class, the methods are identified

by analyzing the sequence diagrams of the following use-cases.

Deposit Checking

Deposit Savings

Withdraw Checking

Withdraw more from Checking

Withdraw Savings

Withdraw Savings denied

Checking Transaction History

Savings Transaction History

3.Identifying Relation

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