of 21
8/3/2019 introduction of databse
1/21
Lecture 1: Database Systems
Lecture 1
Introduction to Databases
8/3/2019 introduction of databse
2/21
Data and Information Data: stored representations of meaningful objects
and events Structured: numbers, text, dates
Unstructured: images, video, documents
Information: processed data for increasingknowledge
Shared collection of logically related data (and adescription of this data), designed to meet the
informational needs of an organization.
Metadata: data that describes the propertiesand context of user data
Lecture 1: Database Systems
8/3/2019 introduction of databse
3/21
Summarized data
Graphical displays turn data into useful information
that managers can use for decision making and
interpretation
8/3/2019 introduction of databse
4/21
Types of Database
Centralized Distributed
Decentralized
Centralized Databases
All data located at central site.
Users at remote sites may generally access thedatabase using communication facilities.
Provides greater control over accessing andupdating data than distributed databases.
More vulnerable to failure since they depend onthe availability of the resources at the central site.
8/3/2019 introduction of databse
5/21
Types of Centralized Databases
Personal Computer (PC) DatabaseThey normally have a single user who creates
the database, updates and maintains the data,
produces reports and displays.Often database supports one application, or at
least a limited number of applications.
Common applications are in small businesses.Typical applications include simple accounting,
inventory management, and customer billing.
8/3/2019 introduction of databse
6/21
Types of Centralized Databases CENTRAL COMPUTER DATABASES
The data that most applications in largeorganizations access is stored on a central
computer.
users at remote locations can access thedatabase using terminals and data
communication links.
Depending on the size of the organization,the central computer is usually a mainframe
or a minicomputer.
8/3/2019 introduction of databse
7/21
Central Computer Database
They often involve very large, integrated
databases that must be accessed by a large
number of users.
Usage is often intense, with several hundred
transactions per second being processed.
Typical applications include airline reservationsystems, financial institutions, and express
delivery companies.
8/3/2019 introduction of databse
8/21
8/3/2019 introduction of databse
9/21
Distributed Databases
DISTRIBUTED DATABASES It is a single logical database that is spread
physically across computers in multiple
locations.Types
Homogeneous Distributed Databases
Heterogeneous Distributed Databases
8/3/2019 introduction of databse
10/21
Homogeneous Distributed Databases
The term homogeneousmeans that the database
technology is the same (or at least compatible) at each
of the locations and that the data at the various
locations are also compatible. For a database to be homogeneous, following
conditions would probably exist:
The computer operating systems used at each of the locations
are the same, or at least they are highly compatible.
The data models used at each of the locations are the same
(relational model usually used).
8/3/2019 introduction of databse
11/21
Homogeneous Distributed Databases
The database management systems used at each of
the locations are the same, or at least they are highly
compatible.
The data at the various locations have commondefinitions and formats.
They simplify the sharing of data among the
various users.They represent the design goal for distributed
databases.
8/3/2019 introduction of databse
12/21
Heterogeneous Distributed Databases
In most organizations, databases evolve over aperiod of time without careful guidance or planning.
Different computers and operating systems may beused at each of the locations.
Different data models and database managementsystems are very common.
To complicate matters further, the data across thelocations are often incompatible.
Sooner or later, the users at various locationsdiscover that they need to share the data, despite theincompatibilities.
8/3/2019 introduction of databse
13/21
Heterogeneous Distributed Databases One solution is to develop a completely new
database that integrates all of the existing systems;
however, this is often not technically or economically
feasible.
Instead, the databases are sometimes linkedtogether.
The result is a set of heterogeneous databases (the
termfederated
databases is also sometimes used). Such a system generally limits the types of
processing that users may perform: for example, a
user at one location may be able to read but not
update the data at another location.
8/3/2019 introduction of databse
14/21
Decentralized Database
Decentralized Database
Collection of independent databases
8/3/2019 introduction of databse
15/21
Case Study of Pine Valley Furniture
Company
Manual System Disadvantages
Stream of paper work and phone call required for
communication Cannot answer the complex queries
Cannot provide summary information
Duplicate data exist
File Processing system/ File Based Systems
Focuses on the data processing needs of individual
department of an organization instead of whole
organization.
8/3/2019 introduction of databse
16/21
File Based System
Collection of application programs thatperform services for the end users (e.g.
reports).
Each program defines and manages its own
data.
The approach is process driven instead of
data driven
8/3/2019 introduction of databse
17/21
8/3/2019 introduction of databse
18/21
Disadvantages of File Processing Separation and isolation of data
Each program maintains its own set of data.
Users of one program may be unaware of potentially useful dataheld by other programs.
Duplication of data Same data is held by different programs.
Wasted space and potentially different values and/or differentformats for the same item.
Fixed Queries/Proliferation of application
programs Programs are written to satisfy particular functions.
Any new requirement needs a new program.
Data Inconsistency
8/3/2019 introduction of databse
19/21
Disadvantages of File Processing
Limited Data Sharing
No centralized control of data
Lengthy Development Times
Programmers must design their own file formats
Poor Enforcement of Standard
Synonym
Homonym
Excessive Program Maintenance
80% of information systems budget
8/3/2019 introduction of databse
20/21
SOLUTION:
The DATABASE Approach
Central repository of shared data
Stored in a standardized, convenient
form Logically related data comprises entities,
attributes, and relationships of an
organizations information.
Data Driven Approach
8/3/2019 introduction of databse
21/21
Database Management System
A software system that is used to create,maintain, and provide controlled access to userdatabases
Order FilingSystem
InvoicingSystem
PayrollSystem
DBMSCentral database
Contains employee,order, inventory,
pricing, andcustomer data
