Chapter 1 Overview of Database Concepts

Chapter 1 Oracle9i: SQL 1

Chapter 1Overview of Database Concepts


Chapter Objectives

• Identify the purpose of a database management system (DBMS)

• Distinguish a field from a record and a column from a row

• Identify the basic components of an Entity-Relationship Model

• Define the three types of relationships that can exist between entities


Chapter Objectives

• Explain the purpose of normalization

• Describe the role of a primary key

• Identify partial dependency and transitive dependency in the normalization process


Chapter Objectives

• Explain the purpose of a foreign key

• Determine how to link data in different tables through the use of a common field

• Explain the purpose of a structured query language (SQL)


Database Terminology

• Database – logical structure to store data

• Database Management System (DBMS) – software used to create and interact with the database


Database Components

• Bit (0 or 1) is the smallest data unit. • A few bits (usually 8) can be organized into

a byte. • Each byte represents a character that is the

basic building block of information. • Field• Record• File


Database Components - Character

• Basic unit of data

• Can be a letter, number, or special symbol


Database Components - Field

• A group of related characters

• Represents an attribute or characteristic of an entity

• Corresponds to a column in the physical database


Database Components - Record

• A collection of fields for one specific entity

• Corresponds to a row in the physical database


Database Components - File

• A group of records about the same type of entity

File (a table) Field A Field B Field C ……..

Record 1

Record 2

Record 3

Record 4

…….


What Are Relations

• A Relational DB is a collection of relations• A relation is a two-dimensional table that has the

following characteristics– Rows contain data about an entity– Columns contain data about attributes of the entity– Cells of the table hold a single value– Each column has a unique name– The order of the columns is unimportant– The order of the rows is unimportant– No two rows may be identical


What Are Relations

• Interchangeably Used Terms in Relational Database– table = file = relation– row = record= tuple – column = field = attribute


Components Example


The Customers File/Table/Relation

• CUSTOMERS

Name Address City State …….

Customer A John 123 5th St. Huntsville AL …….

Customer B …… ………. ………… …. …….

Customer C

Customer D

…….


Review of Database Design

• Systems Development Life Cycle (SDLC)

• Entity-Relationship Model (E-R Model)

• Normalization


Systems Development Life Cycle (SDLC) 5 Phases

• Systems investigation – understanding the problem

• Systems analysis – understanding the solution

• Systems design – creating the logical and physical components


Systems Development Life Cycle (SDLC)

• Systems implementation – placing completed system into operation

• Systems maintenance and review – evaluating the implemented system


Entity-Relationship Model (E-R Model)

• Used to depict the relationship that exists among entities.

• Entity Definitions– An object of interest to the business– A class or category of thing– A named thing or a thing of significance about

which the business needs information– Entity instance is the representation of a

particular entity. Attribute is a characteristic of an entity.


Entities: Examples

COURSE STUDENTINSTRUCTOR

codenamefeelength

namephone no.

namephone no


E-R Model Symbols


Relationships: An Example

taken by

enrolled in

STUDENT COURSE

Each STUDENT may be enrolled in one or more COURSES

Each COURSE may be taken by one or more STUDENTS


Relationships

• The following relationships can be included in an E-R Model:– One-to-one

– One-to-many

– Many-to-many


One-to-one Relationship

• Each occurrence of data in one entity is represented by only one occurrence of data in the other entity

• Example: Each individual has just one Social Security Number (SSN) and each SSN is assigned to just one person


One-to-many Relationship

• Each occurrence of data in one entity can be represented by many occurrences of the data in the other entity

• Example: A class has only one instructor, but each instructor can teach many classes


Many-to-many Relationship

• Data can have multiple occurrences in both entities

• Example: A student can take many classes and each class is composed of many students

• Can not be included in the physical database


Relationship Types: More ExamplesRelationship Types: More ExamplesMany-to-One

One-to-One

Many-to-Many


Many-to-One RelationshipsMany-to-One Relationships

CUSTOMER SALES REPRESENTATIVE

assigned to

visited by


Many-to-Many RelationshipsMany-to-Many Relationships

PATIENT HEALTH CARE WORKER

assigned to

attended by


One-to-One RelationshipsOne-to-One Relationships

BICYCLE RIDER

the rider

is ridden by


Entity-Relationship Model

• An entity is usually represented as a square or rectangle.

• A line between two entities depict their relationships (a dashed line for optional relationship)– One-to-one: straight line– One-to-many: a straight line with a “crowfoot” at

the “many” end.– Many-to-many: a straight line with a “crowfoot”

at each end.


Example E-R Model


Normalization

• Determines required tables and columns for each table

• Multi-step process. Application of a series of rules that gradually improve the design

• Used to reduce or control data redundancy


Unnormalized Data

Contains repeating groups in the Author column in the BOOKS table


First-Normal Form (1NF)

• Primary key is identified– Primary key is a field or a set of fields

(composite PK) that serve to uniquely identify each record in a table. e.g. the SSN field in a table that contains students’ record.

• Repeating groups are eliminated. Single valued attributes only


Primary Keys

• Primary key– Value must be unique for each record– Serves to identify the record– Present in every record– Can’t be NULL– Usually numeric


Candidate Keys

• Candidate key

– Any field that could be used as the primary key

– Should be a unique, unchanging numeric field


Surrogate Keys

• Surrogate key: created to be the record’s primary key identifier when no suitable primary key exists

• Surrogate key has no real relationship to the record to which it is assigned, other than to identify the record uniquely

• Developers configure the database to generate surrogate key values automatically

• Surrogate keys are always numerical fields


Foreign Keys

• Foreign key: a field in a table that is a primary key in another table

• Foreign key creates a relationship between the two tables

• Foreign key value must exist in the table where it is a primary key



Composite Keys

• Composite key: a unique key that you create by combining two or more fields

• Usually comprised of fields that are primary keys in other tables


First-Normal Form (1NF)

ISBN and Author columns together create a composite primary key


Composite Key-P.D.

• More than one column is required to uniquely identify a row

• Can lead to partial dependency - a column is only dependent on a portion of the primary key


Second-Normal Form (2NF)

• Partial dependency must be eliminated– Break the composite primary key into

two parts, each part representing a separate table


Second-Normal Form (2NF)

BOOKS table in 2NF


Third-Normal Form (3NF)

Publisher contact name has been removed


Summary of Normalization Steps

• 1NF: eliminate repeating groups, identify primary key

• 2NF: table is in 1NF and partial dependencies eliminated

• 3NF: table is in 2NF and transitive dependencies eliminated


Linking Tables

• Once tables are normalized, make certain tables are linked

• Tables are linked through a common field• A common field is usually a primary key in

one table and a foreign key in the other table

• A foreign key is a column that is a primary key of another table


Linking Tables

• For every value of a foreign key there is a primary key with that value

• A foreign key can never be null

• A primary key must exist before the foreign key can be defined



JustLee Books’ Database

Assumptions– No back orders or partial shipments– Only US addresses– Shipped orders are purged (deleted) at the end

of the month


Structured Query Language (SQL) and DBMS

• Data sublanguage • Structured Query Language (SQL) is a data

sublanguage that has constructs for defining and processing a database

• It can be – Used stand-alone within a DBMS command– Embedded in triggers and stored procedures– Used in scripting or programming languages

• All DBMS use some variation of the standardized ANSI-SQL. (Oracle SQL Plus)


Structured Query Language (SQL) and DBMS

• SQL was developed by IBM in late 1970s• SQL-92 was endorsed as a national standard by

ANSI in 1992• Data Definition Language (DDL) is used to define

database structures• Data Manipulation Language (DML) is used to

query and update data• DBMS: Database Management System• Examples of DBMS: Oracle, DB2, Microsoft

Access, SQL Server


Client/Server DBMS

Client/server database

• Takes advantage of distributed processing and networked computers by distributing processing across multiple computers

• DBMS server process runs on one workstation, and the database applications run on separate client workstations across the network


Client/Server DBMS

• Preferred for database applications that retrieve and manipulate small amounts of data from databases containing large numbers of records because they minimize network traffic and improve response times

• Organizations generally use a client/server database if the database will have more than 10 simultaneous users and if the database is mission critical


Client/Server Database Architecture


The Oracle9i Client/Server Database

• All Oracle server- and client-side programs use Oracle Net, a utility that enables the network communication between the client and the server


Oracle DBMS

• Oracle is the world’s most popular DBMS• It is a powerful and robust DBMS that runs on

many different operating systems• Oracle DBMS engine: Personal Oracle and

Enterprise Oracle• Example of Oracle products

– SQL*Plus: a utility for processing SQL and creating components like stored procedures and triggers


Oracle SQL *Plus

• Oracle SQL*Plus or the Oracle Enterprise Manager Console may be used to manage an Oracle database

• SQL*Plus is a text editor available in all Oracle• Case-insensitive• The semicolon (;) terminates a SQL statement• The right-leaning slash (/) executes SQL statement

stored in Oracle buffer

Documents

Chapter 1 Overview of Database Concepts