Object Oriented Database and UML

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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 Benefits

• Object orientation is a modeling and development
  methodology based on object-oriented (OO)
  concepts.
• Definition of Object OrientationA 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 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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The Evolution of OO Concepts

• 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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The Evolution of OO Concepts

• 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 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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Object-Oriented Concepts

• Objects Components and Characteristics
• An 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-Oriented Concepts

• Object Identity
• The objects 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 objects 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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Object-Oriented Concepts

• 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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Object Attributes
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Object-Oriented Concepts

• Object State
• The object state is the set of values that the
  objects attributes have at a given time.
• If we change the objects state, we must change
  the values of the object attributes.
• To change the objects attribute values, we must
  send a message to the object.
• This message invokes a method.

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Object-Oriented Concepts

• 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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Object-Oriented Concepts

• 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 objects internal details
  (attributes and methods) is known as
  encapsulation.
• An object may send messages to change or
  interrogate another objects state. (See Figure
  11.3)

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Objects Send Messages To Each Other
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Object-Oriented Concepts

• 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 Living Backbone
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Representation Of The Class Student
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Object-Oriented Concepts

• Protocol
• The classs collection of messages, each
  identified by a message name, constitutes the
  object or class protocol.
• The protocol represents an objects public
  aspect i.e., it is known by other objects as
  well as end users.
• The implementation of the objects structure and
  methods constitutes the objects 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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Public and Private Aspects Of An Object
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Flashlights Demo

• Example of basic OO concepts

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OO Summary Object Characteristics
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Object-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 Hierarchy
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Object-Oriented Concepts

• 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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Object-Oriented Concepts

• 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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Motor Vehicle And Bicycle Instance Variables
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Object-Oriented Concepts

• 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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Employee Class Hierarchy Method Override
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Employee Class Hierarchy Polymorphism
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Object-Oriented Concepts

• 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 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 methods 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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OO And E-R Model Components
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OODM 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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An Invoice Representation
But remember the object has methods attached to
it too.
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OODM and Previous Data Models

• 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 methods implementation from other objects
  and the user.

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OODM and Previous Data Models

• 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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OODM and Previous Data Models

• 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 DBMS
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The Thirteen OODBMS Rules
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How 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.
• DBAs role is likely to change with more
  programming responsibilities.
• Lack of standards affects OO database design.

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OODBMS 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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OODBMS Advantages and Disadvantages

• 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.

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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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How OO Concepts Have Influenced the Relational
Model

• Philosophy that guides the relational models
  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 Worlds Modeling Experts in a
  room and push pizza under the door every 5 hours
  but dont 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
0..M
0..1
Package
Model
0..1
0..
References
Includes
0..
0..
Element
Model Element
Visual Element
1..
0..
Projection
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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 Handle Shape Bulbs OnOff( )
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Associations
An Association
Tools
Flashlight
A Link
Flashlight
Maglight
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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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Associations
0..M
0..1
Package
Model
0..1
0..
References
Includes
0..
0..
Element
Model Element
Visual Element
1..
0..
Projection
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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
Drive
uses
uses
Customer
Service
uses
Repair
Mechanic
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Activity Diagrams

• Represents the activities or behaviors of a
  system.

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Activity Diagram
Look up Person SELECT PersonID, Name FROM Person
WHERE p.PersonID a.PersonID
Identify Person Name
Supply SSNa.PersonID
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Activity Diagram With Swimlanes
Teacher
Student
Board
Teach
Learn
Supervise Exam
Take Exam
Evaluate
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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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Sequence Diagrams
Caller
Phone
Recipient
Picks Up
Dial Tone
Dial
Ring
Ring
Picks Up
Hello
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UML Patterns

• How humans solve problems.
• Look at a problem.
• Try to find an analog in our experience.
• 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
The Data and AnyOperation elements represent the
class-specific attributes an d operations
1..1
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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
1
M
Table1
Table2
Has
(x,y)
(x,y)
Key2
Key1
Key1
Attr1
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Generating SQL From UML
A A1 String A2 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