Uml - Class Diagram

Lecture 02: Class diagram Doan Trung Tung, PhD OO AD

OBJECT-ORIENTED ANALYSIS AND DESIGN

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PLAN

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Class diagram  Relationships  From requirements to Class diagram

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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What is a Class Diagram?  A class diagram describes the types of objects in the system and the various kinds of relationships that exist among them.  A graphical representation of a static view on static elements.  Richest notation in UML

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Objects

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Objects have three responsibilities:

o What they know about themselves – (e.g., Attributes)

o What they do – (e.g., Operations) o What they know about other objects – (e.g., Relationships)

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Class

OBJECT-ORIENTED ANALYSIS AND DESIGN



A class is a template (specification, blueprint) for a collection of objects that share a common set of attributes and operations. MovieClubMember

Class

attributes operations

Objects

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Class notation in class diagram

OBJECT-ORIENTED ANALYSIS AND DESIGN

Class name

private Attributes

protected public

Methods

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Generalization relationship  A generalization connects a subclass to its superclass. It denotes an inheritance of attributes and behaviors from the superclass to the subclass and indicates a specialization in the subclass of the more general superclass.  Can be viewed as “is a” relationship

Student

Person

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Generalization relationship  UML permits a class to inherit from multiple superclasses, although some programming languages (e.g., Java) do not permit multiple inheritance.

Student

Employee

TeachingAssistant 8

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Generalization relationship

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Abstract class Shape draw()

Circle

Rectangle

draw()

draw() 9

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Generalization relationship

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Discriminator Discriminator Doctor Female role

Person Male

Gender {complete}

Nurse

patient Physicaltherapist Patient 10

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Associations relationship

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Relationships between instances (objects)  Association describes a link, a link being a connection among objects between classes.

 Can be viewed as “has a” relationship

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Associations relationship

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Properties o Name o Role › The specific role of the association

o Multiplicity › Indicates the number of objects that are connected

o Type › Plain association, aggregation, composition

o Direction

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Associations

OBJECT-ORIENTED ANALYSIS AND DESIGN

Example: A Person works for a Company Role

employee

employer

Person

Company works for Association Name

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Associations  Multiplicity: specify properties of the number of links that can exist between instances (objects) of the associated classes. Association name

Class1

multiplicity

multiplicity

Class2

 Multiplicity notation o* o5 o 5..8 o 5..*

 0, 1, or more  5 exactly  between 5 and 8, inclusive  5 or more 14

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Associations

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Multiplicity example o A Student can take up to 5 Courses. o Student has to be enrolled in at least one course. o Up to 300 students can enroll in a course. o A class should have at least 10 students.

Student 10..300

takes

1..5

Course

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Associations

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Multiplicity example o A teacher teaches 1 to 3 courses (subjects) o Each course is taught by only one teacher. o A student can take between 1 to 5 courses. o A course can have 10 to 300 students.

Teacher

1

teaches

1..3

Course

1..5

takes

Students 10..300

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Self association  An association that connects a class to itself is called a self association.

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Employee

manager Responsible for 0..10

worker

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Multi associations

OBJECT-ORIENTED ANALYSIS AND DESIGN

 A cricket team has 11 players. One of them is the captain.  A player can play only for one Team.  The captain leads the team members. Team Member

Captain

Player

1

0..1

Team

10

11 1

member of

1

Captain

Leads 18

OBJECT-ORIENTED ANALYSIS AND DESIGN

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Aggregation  A specialized form of Association in which a whole is related to its part(s)  Can be viewed as a “part of” relationship o Whole – parts o Container – contents o Group - members

Can they be association?

Engine Car Transmission 19

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Composition

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Special Aggregation

Can they be aggregation?

 Strong ownership

Scrollbar

Window

Titlebar

Menu

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How to identify aggregation / composition?

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Lifetime of part is bound within lifetime of composite o There is a create-delete dependency

 There is an obvious whole-part physical or logical assembly  Some properties of composite propagate to parts (e.g., location)

 Operations applied to composite propagate to parts (e.g., destruction, movement, recording)

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Why aggregation / composition?

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Assists in identification of a creator  Operations applied to whole should usually propagate to parts

 Identifying whole - parts supports encapsulation

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Dependency  Change in specification of one class can change the other class. This can happen when one class is using another class.  Always directed  Caused by class methods o local variable, parameter, return value

Circle Point Move(p:Point) 23

OBJECT-ORIENTED ANALYSIS AND DESIGN

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Dependency  Dependency relationship can be used to show relationships between classes and objects

circleA:Circle Circle

circleB:Circle 24

OBJECT-ORIENTED ANALYSIS AND DESIGN

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Realization (implementation)  A realization relationship indicates that one class implements a behavior specified by another class (an interface or protocol).  An interface can be realized by many classes.  A class may realize many interfaces.

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Realization

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Example Keyboard brandName numOfKeys

<> TypeWriter

ctl() pageDown()

keyStroke()

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Constraint rules and Notes  Constraints and notes annotate among other things associations, attributes, operations and classes.  Constraints are semantic restrictions noted as Boolean expressions.

Customer id: long { value > 0 }

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* { total < $50 }

Constraint

Order

may be canceled

Note 27

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Common mistakes / confusions

OBJECT-ORIENTED ANALYSIS AND DESIGN

When drawing Class Diagram o Draw classes immediately o Hard to differentiate relationships › Associations or › Aggregation or › Composition?

o Attributes or classes? o Inheritances or Interfaces? o Draw all dependencies? o…

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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From user requirements to Class Diagram “A class diagram describes the types of objects in the system and the various kinds of static relationships that exist among them”  Make a list of objects found in user requirements  Group similar objects into class  Define relationships between each two classes o Multiplicity o Type (generalization, association, realization, dependency) o Name, direction, … 29

OBJECT-ORIENTED ANALYSIS AND DESIGN

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User requirements … Zounds international (Audiovisual sales) Has A number of (sub) divisions such as Purchasing, NetSales, Stock, Retail etc. ‘Retail’ has outlets (e.g. in Malls and High street stores). NetSales has both ‘Hard’ (CDs, DVDs…) and ‘soft’ (downloads) sales. Retail and Netsales co-operate to produce ‘Personal mixes’ that they burn onto CDs to produce items for individual customers. Customers may open an account to facilitate the payment for multiple transactions or they may just buy goods in individual purchases paying by cash, cheque or card. The staff selling the good are recorded. 30

OBJECT-ORIENTED ANALYSIS AND DESIGN

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User requirements … Zounds international (Audiovisual sales) Has A number of (sub) divisions such as Purchasing, NetSales, Stock, Retail etc. ‘Retail’ has outlets (e.g. in Malls and High street stores). NetSales has both ‘Hard’ (CDs, DVDs…) and ‘soft’ (downloads) sales. Retail and Netsales co-operate to produce ‘Personal mixes’ that they burn onto CDs to produce items for individual customers. Customers may open an account to facilitate the payment for multiple transactions or they may just buy goods in individual purchases paying by cash, cheque or card. The staff selling the good are recorded. 31

OBJECT-ORIENTED ANALYSIS AND DESIGN

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User requirements … A sub-division may also be a parent division e.g. Zounds UK is a sub-division of Zounds international but also a parent of Zounds Sweet (specialising in musical confectionary). ZI has no parent division. Retail staff display and sell traditional stock items (CD, DVD) in the retail outlets to customers (these people may also be staff). The netSales staff maintain and sell copies of ‘softstock’ (digitally encoded mediaware that they are licensed to distribute) direct to customers (or staff). The company’s retail outlets purchase ‘SoftStock’ for the mixes. 32

OBJECT-ORIENTED ANALYSIS AND DESIGN

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User requirements … A sub-division may also be a parent division e.g. Zounds UK is a sub-division of Zounds international but also a parent of Zounds Sweet (specialising in musical confectionary). ZI has no parent division. Retail staff display and sell traditional stock items (CD, DVD) in the retail outlets to customers (these people may also be staff). The netSales staff maintain and sell copies of ‘softstock’ (digitally encoded mediaware that they are licensed to distribute) direct to customers (or staff). The company’s retail outlets purchase ‘SoftStock’ for the mixes. 33

OBJECT-ORIENTED ANALYSIS AND DESIGN

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Objects • Divisions • Subdivisions • Retails • Netsales • Purchasings • Stocks • Transactions • Purchases

• Hard sales • Soft sales • CDs • Mixes • Items • Goods • DVD

• Customers • Staff • Retail staff • Netsale staff

• Accounts

• Cheque • Cash • Card 34

OBJECT-ORIENTED ANALYSIS AND DESIGN

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Classes

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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User requirements … The divisions and subdivisions each have a single manager and may have staff. Staff are employed by Zounds international and are assigned to exactly one division. There are many types of staff and their assignment/role (Cleaner, NetSales, Manager) may vary during their time with ZI. All subdivisions have only one parent division but parent divisions may have many subdivisions. Theoretically all the parent divisions have control over all their subdivisions, though in practice this is seldom enforced for the mundane ‘day-to-day’ running of the company. All Sub-divisions are cost centres, maintaining their own accounts but constrained to follow a centralised accounting model with a standard way of maintaining the balance and transaction history and recording transactions. 36

OBJECT-ORIENTED ANALYSIS AND DESIGN

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User requirements … The divisions and subdivisions each have a single manager and may have staff. Staff are employed by Zounds international and are assigned to exactly one division. There are many types of staff and their assignment/role (Cleaner, NetSales, Manager) may vary during their time with ZI. All subdivisions have only one parent division but parent divisions may have many subdivisions. Theoretically all the parent divisions have control over all their subdivisions, though in practice this is seldom enforced for the mundane ‘day-to-day’ running of the company. All Sub-divisions are cost centres, maintaining their own accounts but constrained to follow a centralised accounting model with a standard way of maintaining the balance and transaction history and recording transactions. 37

OBJECT-ORIENTED ANALYSIS AND DESIGN

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Classes and relationships

Do you agree with type of associations?

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Hidden objects/classes

OBJECT-ORIENTED ANALYSIS AND DESIGN

 Web pages  Windows

Remember class UITool?

 Dialogs

 “Data Access” Classes …

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Exercise The ABC bookstore offers a Web system that allows its customers to search, reserve, buy and rent books online. Any customer can visit the bookstore’s official Web site to search for book details, but only the registered customers (hereinafter, members) can reserve, buy and rent books online. The required information for a membership is the customer’s detail information such as name, address, a unique social ID, phone number, e-mail address, and credit card number. Once the registration is completed, the system will send the confirmation notification to the customer’s e-mail address. The ABC bookstore offers services for both hard-copied books and electronic books. The rental service is applied for hard-copied books only. For hard-copied books, a customer can search for book information and reserve the books that he/she wants to buy or rent. The reserved time is 1 day. After the customer made the reservation, he/she must go to the bookstore to pick up the books within the reserved time. Otherwise, the reserved books will be released to other customers. To pick up the books, the customer must present the reservation number to the bookstore’s staff and pay for the books.

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OBJECT-ORIENTED ANALYSIS AND DESIGN

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Exercise The rental period is 7 days for each book. To return the books, the customer can either go to the bookstore during its office hours (8:00 to 22:00) to return them to the staff at the counter service, or use an automated self-service book return box that is located in front of the bookstore and is available for 24 hours. The book return box has a barcode reader attached to it. The customer has to use the bar code reader to scan a barcode of each book and then put the book into the book return box. If the customer returns the books later than the return date, he/she will be charged at $10 per day per book via his/her credit card. The late-returned fee will be shown in his/her membership account. In case of buying books online (both hard-copied books and electronic books), the customer must make payment using his/her credit card and also provide a shipping address for the books delivery. Draw class diagram (use CRC first). Make your own assumptions if needed 41