1. Database Design – Lecture 11
Introduction to Object Oriented Database Design

2. Lecture Objectives Why Object Oriented Approach? Objects Classes
Universal Modeling Language (UML)

3. Why Object Oriented Approach?
Advances in application development drove the object oriented approach
Applications are more complex - graphical user interfaces utilizing diverse data types such as sound, video and text
Applications are based on ‘object’ patterns that have been developed and tested - reusability

4. Why Object Oriented Approach?
Object Oriented Databases differ from Relational Databases but there are similarities:
Relational model emphasizes an entity and it’s attributes and keeps separate the data manipulation
Object Oriented model emphasizes attributes and data process – encapsulating both into a single object

5. Why Object Oriented Approach?
Self-contained objects can be reused and moved around with relative ease
Supports direct many-to-many relationships
OO databases are navigational - Access to data is through relationships stored within the data themselves (remember hierarchical and network databases?)
Not well suited to ad hoc queries

6. Why Object Oriented Approach?
Two types of OO Databases
Pure object-oriented - based solely on the object-oriented data model (I.e. CA – Jasmine)
Hybrid object oriented – primarily relational – stores objects in relations (this is what we will focus on)

7. Lecture Objectives Why Object Oriented Approach? Objects Classes
Universal Modeling Language (UML)

8. Objects
“An object is an abstract representation of some real world entity that has a unique identity, embedded properties, and the ability to interact with other objects and act upon itself” (text)
It is a software construct that encapsulates state and behavior

9. Objects
Each of these objects has a unique identity but they share common general characteristics such as name, address, date of birth

10. Objects Objects are described by attributes or instance variables
Each attribute has a unique name, a base data type (integer, string etc) and a domain (constraint)
An object’s attribute can be single-valued or multi-valued
An object can reference one or more other objects

11. Base data type is ‘real’ with values between 0.00 and 4.00
* Represents an attribute that references one or more other objects
MAJOR references another object called DEPARTMENT
ADVISOR references another object called PROFESSOR
COURSES_TAKEN references another object called COURSE
COURSE is a collection object because Course is a list of objects

12. Objects
Each object has a unique identifier, called an OID (Object ID) **Note: this is not a primary key
OID is assigned by the system at the moment the object is created and can never be changed
OID does not depend on the object’s attribute values
OID is deleted when the object is deleted and can never be re-used

13. Objects
Note: There is no PK or FK notation in object oriented data design!

14. Objects
State
A set of values that the object’s attributes have at any given time
To change the objects state, you must change the values of the object’s attributes
To change the value of the object’s attributes, send a message to the object
The message will invoke a method

15. Object
Methods
The code that performs a specific operation on the object’s data
Can change the object’s attribute values or can return the value of selected object attributes
An object invokes a method by sending a message
Represents the object’s behavior

16. Lecture Objectives Why Object Oriented Approach? Objects Classes
Universal Modeling Language (UML)

17. Classes
A collection of similar objects with shared structure (attributes) and behavior (methods)
All objects in a class share the same structure and the same methods
Each instance of an object is a class instance or an object instance
Each instance of a CLASS is an OBJECT with a unique OID

18. Classes Class is similar to an Entity in a relational data model
Class contains the common features for all the objects in a class, including their structure and methods
Class is a template to create the object

19. Classes Types of classes generally used:
Entity – these classes reflect real world data which relates to the business requirements
Boundary – these classes handle the communication between the system surrounding and the inside of the system (usually relate to interfaces)
Control – these classes coordinate the events needed to realize the behavior (I.e. they know where to find the data but not how to find it)

20. Classes
We will focus on the Entity class

21. Lecture Objectives Why Object Oriented Approach? Objects Classes
Universal Modeling Language (UML)

22. UML Universal Modeling Language
A methodology to follow to model Object Oriented structures
We will use Rational Rose to document our OO structures
Structure of a class in UML notation:
Class Name
Attributes
Operations
(Methods)

23. UML How are classes identified? Classes are identified for a use case
A use case represents a process with a system
Use case descriptions describe what a use case does. Scenarios describe different paths through a use case

24. UML
Sample Use Case Diagram

25. UML Sample Use Case Description Use Case Specification: Browse Catalog
Brief Description
This use case describes how a shopper can browse the catalog of items that are available to be bid on.
Preconditions
At the moment when the use case begins, the system is displaying the Online Auction Main Page.
Basic Flow
The use case begins when the shopper selects the Browse Catalog option on the Online Auction Main Page.
The system retrieves the list of categories (E1) and the system displays the Category Page with a drop down list of categories and an Exit Button.
If the shopper selects the Exit Button, the system performs Exit (S1).
If the shopper selects an option from the drop down list, the system retrieves all the items for that category (E1) and displays an Item List Page showing a table with item names with a Display Button and an Exit Button.

26. UML To discover classes:
Use existing models (will identify classes, attributes and methods/operations)
Use a category list (will identify classes, attributes)
Use noun phrases (will identify classes, attributes)
Objective is to find the data that is required
We will identify entities as we did for relational – through a business overview and we will document the class diagram in Rational Rose

27. Existing Data Models Already published and can be re-used
Retrieved from:

28. Conceptual Class Category
Category List
Focuses on a list of common categories which emphasis business information system needs
Conceptual Class Category
Examples
Business Transactions
Guidelines: These are critical.
Sale, Payment
Transaction Line items
Guidelines: These are the line items associated with transactions.
SalesLineItem
Product or service related to a transaction or a transaction line item
Guidelines: Transactions are for something (a product or service)
Item
Roles of people or organizations related to the transaction; actors in the use case
Guidelines: We usually need to know about the parties involved in a transactions
Cashier, Customer

29. Noun Filtering Done for each scenario (not for a use case description)
Underline the noun phrases in the scenario
Place the candidate noun phrases into a noun filter table template
Filter the noun phrases through a process of elimination
Draw class diagram

30. UML Sample Scenario with noun filtering System Actor Scenarios
HD Browse Item Scenario
Precondition: At the moment when the scenario begins, the system is displaying the Online Auction Main Page.
Actor
System
Selects the Browse Catalog option on the Online Auction Main Page.
Retrieves the list of categories and displays the Category Page with a drop down list of categories and an Exit Button.
Selects an option from the drop down list
Retrieves all the items for that category and displays an Item List Page showing a table with item names with a Display Button and an Exit Button.
Selects an item and clicks the Display Button.
Retrieves the product name, it’s picture and a description and displays the information on the Item Information Page with a Place Bid Button and an Exit Button.
Clicks the Place Bid Button.
Use case ends and starts the Place Bid use case.

31. UML
Sample
Sequence
Diagram – used to discover methods

32. UML Sample Class Diagram methods/operations relationship
Relationship name
class
attributes
multiplicity

33. UML
Class Syntax
Name – should meaningfully reflect the responsibility of the class
I.e. Customer
Attributes – the set of characteristics necessary to describe the class
I.e. firstName, lastName, initial, dateOfBirth
Each attribute has a unique name and data type
Similar to attributes in relational (columns in a table)
Operations/Methods – what actions can be carried out on an instance of the class
I.e. addDateOfBirth, retrieveLastName

34. UML Attributes Can be of a base data type or an abstract data type
i.e. real, integer, string or character
Subject to a predefined set of operations (i.e. integer base data type can be used for addition, subtraction, multiplication and division)
Can have a domain (constraint)
Abstract data type
User defined
Describes a set of similar objects

35. UML Object Oriented Data Model A conceptual model Drawn in MSVisio
Identify the main entities
Identify attributes (both base data type and abstract data type).
If an abstract data type has attributes of its own, create a new class for that abstract data type and include the attributes in it

36. UML
Sample class:
abstract data types
Base data type

37. Discovering Classes - Example
Sun Life provides insurance plans to employees of Seneca. An employee must register for a plan. Each plan has a list of benefits associated with it (for instance, dental, orthodontic, prescriptions, glasses, long term disability etc). Employees can select which benefits they want (they don’t have to sign up for all of them). Employees can also cover their children (or dependents).

38. UML
Sample Conceptual Class Diagram:
Abstract data type
Base data type

39. UML
Sample Conceptual Class Diagram (with multiplicity):

40. Discovering Classes - Example
Seneca College wants to create a website to allow an alumni or a company to be able to make contributions. These customers will be use an id to track their contributions. Contributions will include customer name, address and phone number. When a contribution is made, the customer can select a specific area for their contribution amount to be directed. For instance, they may want to direct their contribution to the athletic department, student housing or to a specific academic department such as Computer Studies. Customers need to specify whether they want a tax receipt or not and they can either be invoiced for their contribution or they can pay for it by credit card.

41. UML Sample Conceptual Class Diagram:
Abstract data types – refer to another class

42. OO Database Design vs Relational Database Design
Model Phase
OO Model
Content
Relational Model
Conceptual Model
Object Oriented Data Model (OODM) – MSVisio
Major classes; some attributes defined; shows all relationships (including M:N)
Entity Relationship Diagram (ERD) – MSVisio
Major entities; some attributes defined; shows all relationships (may show M:N)
Logical Model
Class Diagram – Rational Rose
Classes; attributes; relationships (can still have M:N)
Entities; attributes; PKs, FKs, relationships (no M:N)
Physical Model
Relational Schema – MSAccess
Tables; attributes, PKs, FKs, all attributes atomic, no MVD