Chapter 1
Introduction
1
Introduction

Definition A database management system (DBMS) is a
general-purpose software system that facilitates the process
of defining, constructing, and manipulating databases for
various applications.

Definition A database is a collection of related data.

Definition Data are known facts that can be recorded and
that have implicit meaning.

Definition File processing systems are business computer
systems which store groups of records in separate files
& used to process business records & produce information.
2
Introduction
DBMS
File Processing Systems
- Data redundancy &
inconsistency
Reduced by ensuring a
physical piece of data is
available to all programs
Data is often duplicated
causing higher storage and
access cost, poor data integrity,
and data inconsistency
- Accessing data
Allow flexible access to
data (e.g., using queries
for data retrievals)
Allow pre-determined access
to data (i.e., complied programs);
application programs are
dependent on file formats
- Concurrent access
Designed to coordinate
multiple users accessing
the same data at the
same time
Designed to allow a file to be
accessed by two programs
concurrently only if both
programs have read-only
access to the file
- Data security &
integrity
High, enforced
Loose, not enforced
3
Data Abstraction

Provides an abstract view of data

Physical level: the lowest level of abstraction
describes the storage structure of data.

Conceptual level: the next-higher level of abstraction
describes the logical structure of the database.

View level: the highest level of abstraction describes
part of the entire database. Many views are
provides for the same database.
4
Database Terminology

Database Schema or Conceptual View: describes the
overall logical structure of the entire database

Database Instance: describes the content of the database

Schema = Type, Instance = Value of a variable
5
Data Independence

The capacity to change the schema definition at one level
without having to change the schema definition at the
next higher level

Physical data independence: capacity to change the
physical schema without having to rewrite the
application programs

Logical data independence: capacity to change the
conceptual schema without having to rewrite the
application programs

logical data independence is more difficult to achieve
than physical data independence
6
Data Models

Describe relationships among data, data semantics, integrity, and
semantic constraints at the conceptual and view levels

I. Object-Based Logic Models



DB is structured in variable-length records

Provide flexible structuring capabilities

Allow explicit specifications of data constraints

Widely used data models: Entity-Relationship and Object-Oriented
II. Record-Based Logical Models

DB is structured in fixed-format records of different types

Three widely used data models: Relational, Hierarchical, and Network
II. Semi-Structured Data Model

Data items of the same type can have different sets of attributes

Widely used data model: XML (Extensible Markup Language)
7
Entity-Relationship (E-R) Model

An object-based Model

A graphical structure (Chapter 7)

Widely used in database design

Consists of real world objects called entities and relationships
among entities

An entity is an distinguishable object with a set of attributes

Entity set is a set of entities of the same type

Relationship set is a set of relationships of the same type

Mapping cardinalities represent the associations among
different entities
8
An Entity-Relationship Diagram
FNAME
Attribute
1
DEPT
A (Binary)
Relationship
ADVISES
ID#
Key
Attribute
An Entity
FACULTY
n
SNAME
STUDENT
ADDR
n
n
MAJOR
Mapping Cardinalities
HAS_TAKEN
IS_TAKING
m
m
COURSE
COURSE#
CRHRS
9
An Entity-Relationship Diagram
FNAME
FACULTY
DEPT
ADVISES
ID#
SNAME
STUDENT
ADDR
MAJOR
HAS_TAKEN
IS_TAKING
COURSE
COURSE#
CRHRS
10
The Object-Oriented Model

An object-based Model


A collection of objects with unique identities



An operation/function can be performed on objects of particular classes
Provide “public interface” for objects of a particular class
Classes consist of objects

Correspond to abstract data type (ADT)
Users can define their own classes

Only way to operate on an object by means of operators defined


Objects can be simple, complex, or made up of other objects
Objects contain methods, i.e., codes operated on objects


Object identity (object-based) vs. value identity (record-based)
Message passing for accessing data in different objects

Apply a given method to a given object by sending a message
11
Object-Oriented Database Systems
Employee
PersonName
EmpName
first
String
Ray
last
String
Ross
SmallInteger
SSNo
11122333
HomeAddress
Address
Salary
Figure. An employee object.
stNumber
SmallInteger
1055
street
String
Alameda
city
String
Gresham
SmallInteger
45558
12
The Relational Model

A record-based Model

Data are organized and stored into 2-dimensional tables
(called relations)

Flexible to use and easy to understand

A relational database schema consists of a number of
relation schemas of the form R(A1, A2, …, An),
where R is a relation name and Ai, 1 < i < n, is
an attribute name.
13
The Relational Model
Relational term
Informal equivalence
Relation
Table
Tuple
Row/Record
Cardinality
# of rows
Attribute
Column/Field
Degree
# of columns
Domain
Set of legal values
Primary Key
Unique Identifier
14
The Relational Database Model
Supplier#
NAME
STATUS
CITY
London
Paris
etc.
Domains
Primary Key
Relation
Supplier Supplier#
S1
S2
S3
S4
S5
SNAME
STATUS
Smith
Jones
Blake
Clark
Adams
20
10
30
20
30
CITY
London
Paris
Paris
London
Athens
Tuples
C
a
r
d
i
n
a
l
i
t
y
Attributes
Degree
15
Data Definition Languages (DDL) &
Data Manipulation Languages (DML)

DDL


Declares the DB schema and compiles the schema into tables
DML

Access/Manipulate (retrieve, insert, delete, & modify) the DB
•
Procedural (or descriptive): specify what is needed and how to
get it
•
Non-procedural (or declarative): specify what is needed but
not how to get it
16
Overall System Structure
17