7 Object Oriented Database and UML MIS 304 Winter 2006.

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Object Oriented Database and UML

MIS 304 Winter 2006

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And now for Something Completely Different…

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Class Objective

• Understand the basic concepts of Object Orientation.

• Understand how the OO approach differs from the Relational approach.

• Apply the concepts of OO to Database management.

• Understand the UML Modeling Language and how it applies to databases

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Object Orientation and Its BenefitsObject Orientation and Its Benefits

• Object orientation is a modeling and development methodology based on object-oriented (OO) concepts.

• Definition of Object Orientation:A set of design and development principles based on conceptually autonomous computer structures known as objects. Each object represents a real-world entity with the ability to interact with itself and with other objects.

• Think of objects as “Nouns” with the “Verbs” already attached to them.

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The History of Object Orientation

Video

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Additional Information on PARC

• Dealers of Lightning: Xerox PARC and the Dawn of the Computer Age , Michael Hiltzik, Texere, 2001, ISBN 1842030000

• Triumph of the Nerds, Robert Cringley, PBS, 1995.

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The Evolution of OO ConceptsThe Evolution of OO Concepts

• From traditional to object-oriented programming (OOP)

– Before OOP, data and procedures were isolated from each other. Data were treated as the passive component, while procedures manipulated the data as the active component.

– Procedural languages (e.g., COBOL) encouraged the rigid distinction between data and procedure.

– In an OOP environment, the programmer asks Objects to perform operations on themselves.

– OO concepts first appeared in some programming languages and set the stage for more refined OO concepts.

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• Main Objectives of Object-Oriented Programming Languages (OOPL)

– To provide an easy-to-use software development environment.

– To provide a powerful software modeling tool for applications prototyping.

– To decrease development time by reducing the amount of code.

– To improve programmer productivity by making that code reusable.

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• Important Attributes of OO Environment

– The data set is no longer passive.

– Data and procedures are bound together, creating an object.

– The object has an innate ability to act on itself.

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Object-Oriented ConceptsObject-Oriented Concepts

• Overview– Objects: Components and Characteristics– Object Identity– Attributes (Instance Variables)– Object State– Messages and Methods– Classes– Protocol– Superclasses, Subclasses, and Inheritance– Methods Overriding and Polymorphism– Abstract Data Types– Object Classification

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• Objects: Components and CharacteristicsAn object is an abstract representation of a real-world entity that has a unique identity, embedded properties, and the ability to interact with other objects and itself.

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• Object Identity

– The object’s identity is represented by an object ID (OID), which is unique to that object.

– The OID is assigned by the system at the moment of the object’s creation and cannot be changed under any circumstance.

– The OID can be deleted only if the object is deleted, and that OID can never be reused.

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Object Identity

• Based on an Object Identifier (OID)• Must be guaranteed to be unique in the space in

which the object exists.• Syntax options

– Dotted 1.2.3.4.5.6.7

– GUID Semi-Random number {}

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• Attributes (Instance Variables)

– Objects are described by their attributes, known as instance variables. (See Table 11.2)

– Attributes have a domain. The domain logically groups and describes the set of all possible values that an attribute can have.

– An attribute can be single valued or multivalued.

– Attributes may reference one or more other objects.

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7Object Attributes

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• Object State

– The object state is the set of values that the object’s attributes have at a given time.

• If we change the object’s state, we must change the values of the object attributes.

• To change the object’s attribute values, we must send a message to the object.

• This message invokes a method.

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• Messages and Methods

– Every operation performed on an object must be implemented by a method.

• Methods represent real-world actions and are equivalent to procedures in traditional programming languages.

– Every method is identified by a name and has a body.

• The body is composed of computer instructions written in some programming language to represent a real-world action.

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• Messages and Methods

– To invoke a method you send a message to the object.

• A message is sent by specifying a receiver object, the name of the method, and any required parameters.

• The internal structure of the object cannot be accessed directly by the message sender. The ability to hide the object’s internal details (attributes and methods) is known as encapsulation.

• An object may send messages to change or interrogate another object’s state. (See Figure 11.3)

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7Objects Send Messages To Each Other

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• Classes

– Objects that share common characteristics are grouped into classes. A class is a collection of similar objects with shared structure (attributes) and behavior (methods).

– Each object in a class is known as a class instance or object instance. (See Figure 11.4)

– Classes are general and extensible

– Example: STUDENT class (See Figure 11.5)

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Class Illustration

Animal

Living

Vertebrates

LivingBackbone

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7Representation Of The Class Student

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• Protocol

– The class’s collection of messages, each identified by a message name, constitutes the object or class protocol.

– The protocol represents an object’s public aspect; i.e., it is known by other objects as well as end users.

– The implementation of the object’s structure and methods constitutes the object’s private aspect.

– A message can be sent to an object instance or the class. When the receiver object is a class, the message will invoke a class method.

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7Public and Private Aspects Of An Object

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Flashlights Demo

• Example of basic OO concepts

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7OO Summary: Object Characteristics

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7Object-Oriented ConceptsObject-Oriented Concepts

• Superclasses, Subclasses, and Inheritance

– Classes are organized into a class hierarchy.

• Example: Musical instrument class hierarchy (Figure 11.8)

– Piano, Violin, and Guitar are a subclass of Stringed instruments, which is, in turn, a subclass of Musical instruments.

– Musical instruments defines the superclass of Stringed instruments, which is, in turn, the superclass of the Piano, Violin, and Guitar classes.

– Inheritance is the ability of an object within the hierarchy to inherit the data structure and behavior (methods) of the classes above it.

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Musical Instruments Class HierarchyMusical Instruments Class Hierarchy

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• Two variants of inheritance:– Single inheritance exists when a class has only one

immediate superclass above it.

• Most of the current OO systems support single inheritance.

• When the system sends a message to an object instance, the entire hierarchy is searched for the matching method in the following sequence:

– Scan the class to which the object belongs.– If the method is not found, scan the superclass.

• The scanning process is repeated until either one of the following occurs:

– The method is found.– The top of the class hierarchy is reached without finding the

message.

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Single Inheritance

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• Two variants of inheritance:– Multiple inheritance allow a class to be derived from several

parent superclasses located above that class.

– Single inheritance exists when a class has only one immediate (parent) superclass above it.

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7Motor Vehicle And Bicycle Instance Variables

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• Method Overriding and Polymorphism– We may override a superclass’ method definition by

redefining the method at the subclass level. (See Figure 11.12)

– Polymorphism allows different objects to respond to the same message in different ways. (See Figure 11.13)

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7Employee Class Hierarchy Method Override

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7Employee Class Hierarchy Polymorphism

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• Object Classification

– A simple object contains only single-valued attributes and none of its attributes refer to another object.

– A composite object contains at least one multivalued attribute and none of its attributes refer to another object.

– A compound object contains at least one attribute that references another object.

– A hybrid object contains a repeating group of attributes, and at least one of the repeating attributes refers to another object.

– An associative object is used to represent a relationship between two or more objects.

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Characteristics of an OO Data ModelCharacteristics of an OO Data Model

• An Object-Oriented Data Model Must:

– Support the representation of complex objects.

– Be extensible; i.e., it must be capable of defining new data types as well as the operations to be performed on them.

– Support encapsulation; i.e., the data representation and the method’s implementation must be hidden from external entities.

– Exhibit inheritance; an object must be able to inherit the properties (data and methods) of other objects.

– Support the notion of object identity (OID).

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How do you apply these concepts to Databases?

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7OO And E-R Model Components

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OODM and Previous Data ModelsOODM and Previous Data Models

• Object, Entity, and Tuple

– An OODM object has additional characteristics such as behavior, inheritance, and encapsulation.

– Such characteristics make OO modeling much more natural than E-R and relational modeling.

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7An Invoice Representation

But remember the object has “methods” attached to it too.

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• Class, Entity Set, and Table– Class is a more powerful concept that allows not only the

description of the data structure but also the description of the behavior.

– A class allows both the concept and the implementation of abstract data types.

• Encapsulation and Inheritance– An object belonging to a class inherits all the properties of its

superclasses.

– Encapsulation hides the data representation and the method’s implementation from other objects and the user.

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• Object ID

– Object ID is not supported in either the E-R model or the relational model.

– The hierarchical and the CODASYL models support some form of ID.

• Relationships

– Relationships in an OODM can be of two types: interclass references or class hierarchy inheritance.

– E-R and relational models use a value-based relationship approach.

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• Access

– E-R and relational models use an ad hoc, set-oriented query language.

– OODM is suited to support both navigational and set-oriented access.

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Object-Oriented DBMSObject-Oriented DBMS

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7The Thirteen OODBMS Rules

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How OO Affects Database DesignHow OO Affects Database Design

• OO database design approach provides both the data identification and the procedures or data manipulation to be performed.

• OO database design forces us to think of data and procedures as a self-contained entity.

• OO design is iterative and incremental in nature.

• DBA’s role is likely to change with more programming responsibilities.

• Lack of standards affects OO database design.

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OODBMS: Advantages and DisadvantagesOODBMS: Advantages and Disadvantages

• Advantages

– More semantic information.

– Support for complex objects.

– Extensibility of data types.

– Improved performance with efficient caching.

– Versioning.

– Faster development and easy maintenance through inheritance and reusability.

– Technology-driven product for next generation DBMS.

– Potential to integrate DBMSs into a single environment.

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• Disadvantages

– Strong opposition from the established players.

– Lack of theoretical foundation.

– Retrogressive to the old pointer systems.

– Lack of standard ad hoc query language.

– Lack of business data design and management tools.

– Steep learning curve.

– Lack of resources.

OODBMS: Advantages and DisadvantagesOODBMS: Advantages and Disadvantages

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How OO Concepts Have Influenced the Relational Model


• New Features for Extended Relational (Object/Relational) Model

– Extensibility of new user-defined (abstract) data types

– Complex objects

– Inheritance

– Procedure calls (rules or triggers)

– System-generated identifiers (OID surrogates)

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• Philosophy that guides the relational model’s enhancements:

– Semantic and object-oriented concepts are necessary to support the new generation of applications.

– These concepts can and must be added to the relational model.

– The benefits of the relational model must be preserved to protect the investment in relational technology and to provide downward compatibility.

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The Next Generation of DBMS

• The next generation of DBMS is likely to incorporate features borrowed from:

– Object-oriented database systems

– Artificial intelligence systems

– Expert systems

– Distributed database

– The Internet

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So how do we model it?

• Need a new modeling methodology that accounts for these new features.

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Unified Modeling Language

MIS 304 Winter 2006

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Class Objective

• Understand the Reasons for the development of a UML

• Apply the concepts of UML to Databases• Be able to construct some simple UML models.

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Tower of Babel

• You have already seen 4 different “Modeling Languages”– The two in the book (actually 4 were mentioned)

– MS Access “Relationships”

– Basic “Objects”

• There are dozens of others.

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Modeling Goals

• One of the goals of modeling is to improve communication.

• When two IT people got together to compare models they often waste a lot of time explaining their models syntax to one another.

• You learn one in school and the organization you work for uses another.

What to do?

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The Solution

Put all of the World’s “Modeling Experts” in a room and push pizza under the door every 5 hours but don’t let them out until they agree on a single way of modeling a “system”.

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The Result - UML

• An “Object Oriented” approach to modeling.• A common modeling notation.• A common modeling language.• Defines several related model notations for

representing all aspects of a system.

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UML Goals

• To represent complete systems, not just software.

• Establish a explicit coupling between concepts and executable code.

• Take into account scaling factors.• Make the model understandable to humans and

machines.

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UML Models

• The Class Model for static structures.• The State model expresses dynamic behavior.• The Use Case describes the requirements of the user.• The Interaction Model represents scenarios and message

flows.• The Implementation Model shows the work units• The Deployment Model provides details that pertain to process

allocation.

And a special subset for Databases

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A UML Model of UML Models

Package

Element

Model Element Visual Element

Model

0..M 0..1

1..* 0..*

Projection

Includes 0..*

0..1 0..*0..* References

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UML Diagrams

• The Diagram provides the reader with a means of Visualizing and manipulating model elements.

• The level of detail is suitable to the Context.• The common building block is the Element.• Mechanisms provide a way to link and describe

the elements.

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UML Diagrams

• Class Diagram • Sequence Diagram • Collaboration Diagram• Object Diagram • Statechart Diagram• Activity Diagram • Use Case Diagram • Component Diagram • Deployment Diagram

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Packages

• Provide a way to partition a model

• Defines a namespace• Packages can be

contained in other packages.

Package Name

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Class Diagrams

• A general way to describe static structure.

• Describes a classic object “class”

• No real change from traditional OO model notation

Class Name

Properties

Operations

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Class Example

• Flashlight class

Flashlight

HandleShapeBulbs

OnOff( )

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Associations

Tools FlashlightAn Association

Flashlight MaglightA Link

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Associations

• Describe how elements are linked together.– 1 One and only one

– 0..1 0 to 1

– M..N Many to many

– 0..* 0 to any integer

– 1..* 1 to any integer

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Package

Element

Model Element Visual Element

Model

0..M 0..1

1..* 0..*

Projection

Includes 0..*

0..1 0..*0..* References

AssociationsAssociations

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Class Hierarchy

Animal

Legs Food

2 Legs 4 Legs Carnivore

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Object Diagrams

• Show a static state.• Primarily used to show context.• Look like Class diagrams.

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Use Case

• Describes how the people involved “Use” the system.

• Simple diagram that lays out the actors interfaces and associations.

• One of the first steps in system design.

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Use Case for Automobile

Customer

Drive

Service

«uses»

«uses»

Mechanic

Repair«uses»

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Activity Diagrams

• Represents the activities or behaviors of a system.

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Activity Diagram

Supply SSNa.PersonID

Look up PersonSELECT PersonID, Name FROM Person WHERE p.PersonID = a.PersonID

Identify Person

Name

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Teacher Student Board

Teach

Learn

SuperviseExam

Take Exam

Evaluate

Activity Diagram With Swimlanes

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Sequence Diagrams

• Used to display interactions between objects.• Focuses on expressing interactions.• Defines the sequence of actions between objects.

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Caller Phone Recipient

Picks Up

Dial Tone

Dial

Ring

Picks Up

Hello

Ring

Sequence DiagramsSequence Diagrams

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UML Patterns

• How humans solve problems.1. Look at a problem.

2. Try to find an analog in our experience.

3. Adapt the analog to our problem.

• In a formal system you can do this in a standardized way.

• In UML these are called “Patterns”• In UML Patterns are identified by a Name.

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UML Database Patterns

• Singleton• Composite• Flyweight• Analysis Patterns

– Party

– Geographical location

– Process

– Document

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Singleton

• The Problem– One object instance

– Used in hierarchy where the entity is part of the structure. (A manager is an Employee)

• The Solution– Single relationship with itself.

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Singleton

Singleton

#Data: Any+Instance( ) Singleton+AnyOperations( ): Any

1

1..1

The Data and AnyOperation elements

represent the class-specific attributes an d

operations

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Composite

• Models the basic “Parent-Child” relationship.• Used things for Organization Charts, Header-

Detail structures or any similar pattern.

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Composite UML

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Composite ERD

Table1 Table2Has

Key2 Key1Key1 Attr1

1 M

(x,y) (x,y)

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Generating SQL From UML

A

A1 : StringA2 : String

SetPrimaryKey(A_Id)

CREATE TABLE A (A_Id Number (5),A1 VARCHAR(),A2 VARCHAR(),PRIMARY KEY(A_Id)

)

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References

• Database Design for Smarties Using UML for Data Modeling, Robert J. Muller, Academic Press, 1999, ISBN 1-55860-515-0

7 Object Oriented Database and UML MIS 304 Winter 2006.

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