Class Diagram Mehwish Shafiq

Class Collection of object that share common properties, attributes, and behavior. Collection of objects with same data structures (attributes) and behavior (Function, code, operation).

Classification & Instantiation Grouping common objects in a class is classification. Instantiation is the Act of creating an instance.

Example

Representing a class Class Name Attributes Methods

Members of a Class Attributes and Methods Their Visibility has 3 types  Public “+”  Private “-”  Protected “#”

Example-Visibility Student - enrolment_no : String - award : String + set_number(number ): int + set_award(award) + get_number() + get_award()

Interface We access objects by calling its methods. Set of method calls available for object are called its interface. Student - enrolment_no : String - award : String + set_number(String n ) + set_award(String a ) + get_number( ) + get_award( )

More about Classes Define classes that collaborate to perform required task. Define classes that deliver required use cases. Defining classes=defining overall system architecture.

Identifying Classes identify the important things mentioned in the text usually described as ‘things of interest in the system’ ‘things of interest’ = things = nouns normally nouns and noun phrases Noun identification process:  underline all nouns and noun phrases  gives a first rough list  refine/analyse/eliminate rough list to produce candidate class list

Refining First Noun List convert plurals to singular  Books > Book remove synonyms  choose one of ‘library-member’ & ‘member of the library’ remove anything vague/ambiguous, or clarify it usually remove events or actions remove anything outside the scope of the system gives list of possible classes

Refining Candidate Class List check relevance/role/need for the class  would Publisher be a class, or just an attribute of Book

Dealing with Uncertainty? if in doubt  keep it in the list?  or not? keeping it in may cause confusion/ambiguity leaving it out may lose information some analysts keep 2 lists  definites and maybes

What kind of things might be classes? real-world tangible things - Book, Copy real-world intangibles - Course, Unit roles - Borrower, Student sometimes (but often not)-> events, interactions  loan, appointment

Actors and classes is an actor a class in the system? Yes, if  system needs to store information about the actor, for example BookBorrower becomes Library_member