Download Slides

Database Management System
• An Information system is a model about
some phenomena in the world - the
Universe of Discourse - (e.g. an
organization)
– retrieves, updates and deletes these facts
– derives other facts from existing ones
• Database:
A database contains a collection of related items
or facts arranged in a specific structure.
OR
A shared collection of logically related data (and
a description of this data), designed to meet the
organization needs.
The most obvious example of a noncomputerized database is a telephone directory.
Three of the most important terms to know
about database are:
• Fields
• Records
• Tables
Types of Databases
• Operational Databases: (Transaction, production
databases) (Example Customer, inventory, HR
database)
• Distributed Databases (Any type of database)
• External Databases (Commercial Online
services – Example full text databases)
• Hypermedia Databases (Hyperlinked pages of
multimedia – set of interconnected multimedia
pages at a website is a database of interrelated
hypermedia page elements, rather then
interrelated data records)
DBMS:
• To make large collections of data useful,
people and organizations use computers
and an efficient data management system.
• A DBMS is a software tool that allows
people to store, access, and process data
or facts into useful information.
Why Use a DBMS?
• Data independence and efficient
access.
• Reduced application development time.
• Data integrity and security.
• Uniform data administration.
• Concurrent access, recovery from
crashes.
Functions of a DBMS

Data storage, retrieval, update

A user-accessible catalog

Transaction support

Concurrency control

Recovery services

Authorization services

Support for data communication

Integrity services

Data independence

Utility services
There are four essential elements of DBMS
• A Modeling Language – Data Model (hierarchical, network, relational
and object models )
• Data Structures (fields, records, files and objects) optimized to deal
with very large amounts of data stored on a permanent data storage
device (which implies relatively slow access compared to volatile
main memory).
• A database query language to allow users to interactively interrogate
the database, analyze its data and update it according to the users
privileges on data.
• Transaction Mechanism: This helps to allow multiple and concurrent
access to the database by multiple users, prevents the manipulation
of one record by two users at the same time, and preventing the
creation of duplicate records.
Purpose of Database Systems
Database management systems were developed to
handle the following difficulties of typical fileprocessing systems supported by conventional
operating systems:
•
•
•
•
•
•
•
Data redundancy and inconsistency
Difficulty in accessing data
Data isolation – multiple files and formats
Integrity problems
Atomicity of updates
Concurrent access by multiple users
Security problems
Database Structures / Models
Hierarchical Structure:
• Early mainframe DBMS packages used it.
• Relationships between records form a
hierarchy or treelike structure.
• Root Record and subordinate levels.
• Relationship among records are 1:M
Network Structure:
• Represents more logical relationships
• Allows M:N relationships among records
• Access to elements by several paths
• Data elements or record can be related to
any number of other data elements.
Relational Model:
• Most widely used.
• All data elements within database are
viewed as being stored in the form of
simple tables.
RDBMS
• A Relational database management system (RDBMS) is a
database management system (DBMS) that is based on the
relational model as introduced by E. F. Codd
• A short definition of an RDBMS may be a DBMS in which data is
stored in the form of tables and the relationship among the data is
also stored in the form of tables.
• presented the data to the user as relations (a presentation in tabular
form, i.e. as a collection of tables with each table consisting of a set
of rows and columns)
• provided relational operators to manipulate the data in tabular form
• Relationships can exist between different tables (1:1, 1:M, M:N)
• Most popular commercial and open source databases currently in
use are based on the relational model.
Entity-Relationship Model
Example of entity-relationship model
social-security
customer-name
customer-street
customer-city
customer
depositor
account-number
balance
account
Relational Model
Example of tabular data in the relational model:
name
Johnson
Smith
Johnson
Jones
Smith
ssn
192-83-7465
019-28-3746
192-83-7465
321-12-3123
019-28-3746
street
Alma
North
Alma
Main
North
city
Palo Alto
Rye
Palo Alto
Harrison
Rye
account-number
A-101
A-215
A-201
A-217
A-201
account-number balance
A-101
500
A-201
900
A-215
700
A-217
750
Data Definition Language
(DDL)
• A Data Definition Language (DDL) is a
computer language for defining data
structures.
• DDL compiler generates a set of tables stored
in a data dictionary
• Data dictionary contains metadata (data
about data)
• Create, Drop, Alter, Referential Integrity
statements (Primary Key, Foreign Key)
• Example: CREATE TABLE employees ( id INTEGER PRIMARY KEY,
first_name CHAR(50) NULL, last_name CHAR(75) NOT NULL, dateofbirth
DATE NULL );
Data Manipulation Language (DML)
• is a family of computer languages used
by computer programs or database
users to retrieve, insert, delete and
update data in a database.
• the most popular data manipulation
language is that of SQL
• Select, Insert, Update, and Delete
• Example: Select first_name from employees;
Data Control Language (DCL)
• A Data Control Language (DCL) is a
computer language and a subset of SQL,
used to control access to data in a
database.
• Examples of DCL commands include:
• GRANT to allow specified users to perform
specified tasks.
• to cancel previously granted or denied
permissions.
Storage Management
• A storage manager is a program module that
provides the interface between the low-level
data stored in the database and the
application programs and queries submitted
to the system.
• The storage manager is responsible for the
following tasks:
– Interaction with the file manager
– Efficient storing, retrieving, and updating of data
Database Administrator
• Coordinates all the activities of the database system;
the database administrator has a good understanding
of the enterprise’s information resources and needs:
• Database administrator’s duties include:
–
–
–
–
–
–
–
Schema definition
Storage structure and access method definition
Schema and physical organization modification
Granting user authority to access the database
Specifying integrity constraints
Acting as liaison with users
Monitoring performance and responding to changes in
requirements
Database Users
• Users are differentiated by the way they
expect to interact with the system.
• Application programmers: interact with
system through DML calls.
• Specialized users: write specialized
database applications that do not fit into the
traditional data processing framework
• Sophisticated users: form requests in a
database query language.
• Naive users: invoke one of the permanent
application programs that have been written
previously
Data Sharing in a Database
Environment
reservation
data
loan data
reservation
program
loan
program
overdue
letters
overdue loans
program
DATABASE
MANAGEMENT
SYSTEM
book
reserv
ation
loan
person
Advantages of Database
Environment
• Sharing of data
• Enforcement of security
• Enforcement of development and maintenance
standards
• Reduction of redundancy
• Avoidance of inconsistency across files
• Maintenance of integrity
• Data independence
• Firm theoretical foundation (for the relational
model)
Disadvantages
•
•
•
•
•
•
size
complexity
cost
Additional hardware costs
Higher impact of failure
Recovery more difficult
Data Planning and Database
Design
• Database development involves data
planning and database design activities
• Data models that support business
processes are used to develop databases
that meet the information needs of users.
Database Design: Scenario
Solution
A Simple scenario to Implement
Residency Accommodations have recently expanded there business.
They provide Hotel rooms and private rooms in Houses /
apartments. Their business processes are carried manually, thereby
causing problems for managers to figure out daily reports covering
different aspects of the business.
Initially as a prototype a simple information system is required for
Residency Accommodations capable of holding records of
customers, accommodation owners, accommodation bookings and
details of each accommodation. The system is intended to handle
day to day normal operations and to support managers specifically
in identifying their customers, owners, bookings and accommodation
details in form of printable system generated reports.