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

Database Design – Lecture 11

Introduction to Object Oriented Database Design

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

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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

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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

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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

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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)

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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

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Objects Each of these

objects has a unique identity but they share common general characteristics such as name, address, date of birth

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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

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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

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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

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Objects Note: There is no PK or FK notation in

object oriented data design!

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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

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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

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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

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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

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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)

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Classes We will focus on the Entity class

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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)

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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

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UML Sample Use Case Diagram

Browse Catalogue

Register as Shopper

Place Bid

Shopper

Logon

Register as Seller

Seller

Add Item

System Clock

Close Bid

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UML Sample Use Case Description

Use Case Specification: Browse Catalog

Brief DescriptionThis use case describes how a shopper can browse the catalog of items that are available to be bid on.

PreconditionsAt the moment when the use case begins, the system is displaying the Online Auction Main Page.

Basic Flow1. The use case begins when the shopper selects the Browse Catalog option on the Online Auction Main

Page. 2. 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. 3. If the shopper selects the Exit Button, the system performs Exit (S1).4. 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.

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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

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Existing Data Models

Already published and can be re-used

Retrieved from: http://www.databaseanswers.org/data_models/bank_and_branches/index.htm

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Category List

Focuses on a list of common categories which emphasis business information system needsConceptual Class Category Examples

Business TransactionsGuidelines: These are critical.

Sale, Payment

Transaction Line itemsGuidelines: These are the line items associated with transactions.

SalesLineItem

Product or service related to a transaction or a transaction line itemGuidelines: Transactions are for something (a product or service)

Item

Roles of people or organizations related to the transaction; actors in the use caseGuidelines: We usually need to know about the parties involved in a transactions

Cashier, Customer

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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

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UML Sample Scenario with noun filtering

Scenarios

HD Browse Item ScenarioPrecondition: At the moment when the scenario begins, the system is displaying the Online Auction Main Page.

ActorSystem

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.

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UML

Sample Sequence Diagram –

used to discover methods

: Shopper : UIControl :

BrowseCatalogControl : Category : Item

1: selectOption()

2: requestRetrieve()3: *retrieve()

5: select()

6: requestRetrieve()


8: *retrieve()

9: display()

10: select()

11: click()


13: retrieve()

14: display()

15: click()

4: display()

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UML

Sample Class Diagram

BrowseCatalogControl

requestRetrieve()

<<control>>

UIControl

selectOption()select()display()click()

<<control>>

Item

itemNamepicturedescription

retrieve()

<<entity>>

Category

requestRetrieve()retrieve()

<<entity>>

1..n

1

1..n

1

has

relationship

Relationship name

multiplicity

class attributes

methods/operations

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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

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UML Attributes

Can be of a base data type or an abstract data type Base 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

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UML Object Oriented Data Model

A conceptual model Drawn in MSVisio1. Identify the main entities2. Identify attributes (both base data type and abstract data type).3. 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

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UML Sample class:

Base data type

abstract data types

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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).

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UML Sample Conceptual Class Diagram:

Abstract data type

Base data type

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UML Sample Conceptual Class Diagram (with

multiplicity):

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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 email 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.

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UML Sample Conceptual Class Diagram:

Abstract data types – refer to another class

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OO Database Design vs Relational Database Design

Model Phase OO Model Content Relational Model

Content

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)

Entity Relationship Diagram (ERD) – MSVisio

Entities; attributes; PKs, FKs, relationships (no M:N)

Physical Model Relational Schema – MSAccess

Tables; attributes, PKs, FKs, all attributes atomic, no MVD

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

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