RDBMS Concepts

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RDBMS Concepts

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Course Prerequisites

A basic understanding of SQL in Oracle Understanding of a procedural language

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To provide an overview of the basic RDBMS Concepts

To provide an insight into the architecture and components of a Database System.

Course Objectives

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Session Outline

RDBMS : Description Evolution of the Database Model Entity Relationship Model Integrity Rules Normalization Integrity Rules ER Diagrams ER Model Relational Algebra Operators Relational Database

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RDBMS Concepts Evolution of the database model Approaches to Data Management

File Based Systems DBMS

The Entity Relationship Model Normalization Relational Algebra Codd ’s Rules ORDBMS

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Needs of Computerized Systems

Management of

Data that needs to be stored

Business functions that need to be performed

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Evolution of the Database ModelFiles based system

1970 1985 1990 19951975 1980 2000

Hierarchical DBMS

Network DBMS

Relational DBMS

Distributed DBMS

Object Oriented

DBMS

Object Relational DBMS

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File-Based SystemsDrawbacks:

Data redundancy and inconsistency

Poor handling of unanticipated queries

Concurrent access anomalies

Security problems

Integrity problems

Application dependent on

Storage structure of data

Access strategy of data

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File-Based Systems

Checking A/c

Application

Checking A/c

Data file(s)

Loan InstallmentApplication

LoanInstallmentData file(s)

Savings A/c

Application

Savings A/c

Data file(s)

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CheckingA/c

Application

(All Data)Data Base

SavingsA/c

Application

LoanInstallmentApplication

DatabaseManagement

System(DBMS)

Any NewApplication

- Integrated- Shared

Database Management SystemsA database is a collection of stored operational data used by application systems of a particular enterprise

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Database Management SystemsFunctions:

Data Definition Data Manipulation

Planned Unplanned

Data Security & Integrity Data Recovery & Concurrency Data Dictionary Maintenance Performance

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Database Management Systems

Physical/ InternalHow the data is stored

[ DATA FILES ]

Conceptual/ LogicalWhat data and How it is organized logically

[ TABLE SPACE, SEGMENTS ]

User/ ExternalWhat the user sees

[ TABLES, VIEWS … ]

3-Level DBMS Architecture

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Database Management SystemsAdvantages:

Minimal Data Redundancy

Data Consistency

Data Integration

Data Sharing

Enforcement of Standards

Application Development Ease

Better Controls

Data Independence

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The Entity Relationship Model

The Entity-Relationship data model is based on a perception of the real world which consists of basic objects called entities and relationships among these objects.

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The Entity Relationship Model

Entity

Attribute

Domain

Relation

Cardinality

Key

Constraint

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ER Model: EntityEntity: Is an object that exists, and is distinguishable from other objects, and about

which data needs to be stored in the system Maybe concrete (person, book) or abstract (holiday, concept)

Hint: Identified by nouns Entity Set is a set of entities of the same type

eg: A set of all persons who are allowed to issue books at the library can be defined as entity set Member.

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ER Model: Attribute and DomainAttribute: (Characteristics) Is a feature which qualifies an entity, and about which data needs to be

stored Maybe concrete (name, identity number) or abstract (status)

eg: A Member has a Member ID, Name, Address

A Book has a Book ID, Name, Author

Domain: (Data Type + Format + Validation) Each attribute has a set of permitted values, called the domain of that

attribute

eg: Status can have any one of these values at a time:

Issued, Available, Lost

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ER Model: RelationshipRelationship: Is an association among several entities, and about which data needs to

be storedeg: A Member requests books from the library

Hint: Identified by Verbs

A relationship set is a set of relationships of the same type

May have descriptive attributes

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ER Model: RelationshipCardinality: Expresses the number of instances of the entity to which another entity can be

associated via a relation. Types:

One to One A copy of a Book can be issued by only one Member at a time

One to Many A Member can issue many Books

Many to Many An author can write many books, and a book can be written by many

authors

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ER Model: KeyKey:

A key is an attribute or set of attributes of an entity which can be used to identify it.

Super Key is a set of one or more attributes which, taken collectively, allows an

entity to be uniquely identified in an entity set Candidate Key

is a super key for which no proper subset is a super key (i.e., a minimal super key)

Primary Key is a candidate key chosen by the database designer as the principle

means of identifying entities within an entity set

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ER Model: KeyKey:

Alternate Key is a candidate key that is not a primary key

Foreign Key is an attribute or set of attributes that exist in one entity and

reference similar attribute(s) in another entity wherein they serve as a primary key

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ER Model: ConstraintsConstraints:

Key Constraints:These are constraints implied by the existence of candidate keys. The table definition includes a specification implying uniqueness of the attributes constituting the primary key or alternate keys. A primary key constraint also implies a no-nulls constraint.

Referential Constraints:Constraints implied by the existence of foreign keys in the table definition.

Other Constraints:Constraints enforcing checks of business logic of the application in the table definition.

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ER Model: Example

Cheques

# Chq No* Cust No.* Amount* Date* Amount* To name0 Comments

# primary key

* mandatory

0 optional

OptionalMandatory

Only oneMany

Cust Account

# Customer No.# Account Type# Account No.* Date opened* Balance0 Last Activity

Has/ Issued from

Legend:

ER Diagram for:Cheques are issued from Customer Account

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ER Model: Example Entity - Cust Account

Attribute - Account No, Date Opened ...

Domain - Date Opened should be valid date

Relation - Cheques are “issued from” Cust account.

Cardinality - Many cheques can be written from the same account

Key - Cheque No. is a Primary Key

Constraint - Amount should be not NULL

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Reducing ER diagrams to Tables

The database should conform to the E-R diagram Each entity should have a table Each table will have as many columns as the number of attributes of the

entity (which are unique in the table) Attributes should conform to their domain characteristics Constraints on attributes can be represented as check constraints, not null

or unique constraints Relationships between entities on should be represented as referential key

constraints or tables

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Reducing ER diagrams to Tables

Tuple:

A row in a table is referred to as a tuple (rhymes with ‘couple’)Example: An instance of a Book - (1, ‘Backup and Recovery’, ‘Rama

Velpuri’)

Properties of Relationships: No duplicate tuples Tuples are unordered Attributes are unordered Attribute values are atomic (cannot be decomposed)

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Integrity Rules

Integrity Rules:

No component of the Primary Key can be null The database must not contain any unmatched foreign key values Issues to consider at design time:

Can the foreign key accept nulls What to do in case of deletes/updates of parent

restrict cascade nullify

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Normalization

Normalization: A relation is said to be in normal form if it satisfies a set of constraints

Universe of relations (normalized and unnormalized)

1NF relations (normalized relations)

2NF relations3NF relations

BCNF (Boyce Codd) relations4NF relations

PJ/ NF (5NF Projection Join) relations

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Normalization

FIRST Normal form (1NF) if it contains atomic values only

SECOND Normal form (2NF) if it is in 1NF and every non-key attribute is dependent on the primary

key

THIRD Normal form (3NF) if it is in 2NF and every non-key attribute is non-transitively

dependent on the primary key

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Normalization

Functional Dependency Unique value of one attribute can always be determined if we know the

value of another.Independent variable (X), dependent variable (Y)invoice number (X) --> Order date (Y)

Total Dependency When both the variables are dependent on each other

Employee number (X) <--> Driving license number (Y)

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Normalization

Full Dependency When one attribute is always dependent on at least two other

attributes Invoice Number (X) Part number (Y) Order Quantity (Z)

Transitive Dependency If Y depends on X and X depends on Y

Invoice (X) --> Customer Number (Y) --> Customer Name (Z)

Course (X) --> Department (Y) --> College (Z)

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NormalizationInvoice Number: 4001Date: 22/5/98

Customer ID: C0051Name: Mr. Babu DaveAddress: B-10, Sada society, Borivali (W), Mumbai - 400 092.

Sr. Part Name Qty Unit QtyNo. No. Price Price------------------------------------------------------------------------1. U90 U-pin box 3 10 302. E12 Big eraser box 2 30 60------------------------------------------------------------------------TOTAL: 90

Terms and conditions: TC035Sales person: S04

ABC Company INVOICE

(NOTE: See the appendix #@)

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Relational Algebra Operators

SELECT

PROJECT

PRODUCT

DIVIDE

JOIN

UNION

INTERSECT

DIFFERENCE

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Relational Algebra OperatorsSELECT employees with department number 10

PROJECT name and salary from employee

dept#=10(DEPT)

name, salary(EMP)

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Relational Algebra OperatorsPRODUCT of employee with departmenta

bxyz

aaabbb

X =xyzxyz

EMP X DEPT

DIVIDE Orders containing item numbers X and Z

xz

aaabb

xyzxy

a=

ord#, Item#(ORD_ITEMS)

Item#(item#=‘X’ or ‘Z’(ITEMS))

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Relational Algebra Operators

a1a2

b1b2

c1c2

b1b2

a1a2

b1b2

c1c2

JOIN of employee with department

EMP DEPT

=

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Relational Algebra Operators

cust# (ORD_JUL) cust#(ORD_AUG)

INTERSECT

cust# (ORD_JUL) - cust#(ORD_AUG)

DIFFERENCE

UNION

ORD_JUL ORD_AUG

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Relational Database A database system may be defined as fully relational

if it supports

relational databases (including concepts of domain and key and the two integrity rules)

a language that is at least as powerful as relational algebra

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