What is database?
Database:
A very large collection of related data
Models a real world enterprise:
Entities (e.g., teams, games / students, courses)
Relationships (e.g., The Celtics are playing in the Final!)
Even
active components (e.g. “business logic”)
DBMS: A software package/system that can be used to
store, manage and retrieve data form databases
Database
System: DBMS+data (+ applications)
Why Study Database:
Shift
from computation to information
Always
true for corporate computing
More
and more true in the scientific world and of course, Web
DBMS
encompasses much of CS in a practical discipline
OS,
languages, theory, AI, logic
Why Databases
Why
not store everything on flat files: use the file system of the OS,
cheap/simple…
Name, Course, Grade
John
Smith, CS112, B
Jim
Gray, CS560, A
John
Smith, CS560, B+
Yes,
but not scalable…
Problem 1
Data
redundancy and inconsistency
Multiple file formats, duplication of information in different files
Name,
Course, Email, Grade
John
Smith, js@cs.bu.edu, CS112, B
Mike Stonebraker, ms@cs.bu.edu,
CS234, A Jim Gray, CS560, jg@cs.bu.edu, A
John Smith,
CS560, js@cs.bu.edu, B+
Why this a problem?
Wasted space
Potential inconsistencies (multiple
formats, John Smith vs Smith J.)
Problem 2
Data
retrieval:
Find
the students who took CS560
Find
the students with GPA > 3.5
For
every query we need to write a program!
We
need the retrieval to be:
Easy
to write
Execute
efficiently
Problem 3
Data
Integrity
No
support for sharing:
Prevent simultaneous modifications
No
coping mechanisms for system crashes
No
means of Preventing Data Entry Errors
Security
problems
Database
systems offer solutions to all the above problems.
A database is a collection of data
elements (facts) stored in a computer in a systematic way, such that a computer
program can consult it to answer questions. The answers to those questions
become information that can be used to make decisions that may not be made with
the data elements alone. The computer program used to manage and query a
database is known as a database management system (DBMS). So a database is a
collection of related data that we can use for
Ø
Defining - specifying types
of data
Ø
Constructing - storing &
populating
Ø
Manipulating - querying, updating,
reporting
A Database Management System (DBMS) is a software
package to facilitate the creation and maintenance of a computerized database.
A Database System (DBS) is a DBMS together with the data itself.
Features
of a database:
Ø
It is a persistent (stored)
collection of related data.
Ø
The data is input (stored) only
once.
Ø
The data is organized (in some
fashion).
Ø
The data is accessible and can be
queried (effectively and efficiently).
DBMS:
•
Collection of interrelated data
•
Set of programs to access the data
•
DMBS contains information about a
particular enterprise
•
DBMS provides an environment that it
both convenient and efficient to use
Database management systems were developed to handle
the following difficulties of typical file-processing 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
Introduction
to Databases
We live in an information age. By this
we mean that, first, we accept the universal fact that information is required
in practically all a used broadly here to mean any organisation of activities
to achieve a stated purpose, including socio-economic activities. Second, we
recognise further the importance of efficiently providing timely relevant
information to an enterprise and of the importance of the proper use of
technology to achieve that. Finally, we recognise that the unparallelled
development in the technology to handle information has and will continue to
change the way we work and live, ie. not only does the technology support
existing enterprises but it changes them and makes possible new enterprises
that would not have otherwise been viable.
The impact is perhaps most visible in
business enterprises where there are strong elements of competition. This is
especially so as businesses become more globalised. The ability to coordinate
activities, for example, across national borders and time zones clearly depends
on the timeliness and quality of information made available. More important
perhaps, strategic decisions made by top management in response to perceived
opportunities or threats will decide the future viability of an enterprise, one
way or the other. In other words, in order to manage a business (or any)
enterprise, future development must be properly estimated. Information is a vital
ingredient in this regard.
Information must therefore be collected
and analysed in order to make decisions. It is here that the proper use of
technology will prove to be crucial to an enterprise. Up-to-date management
techniques should include computers, since they are very powerful tools for processing
large quantities of information. Collecting and analysing information using
computers is
facilitated by current Database Technology, a relatively mature technology which is the subject
of this book.
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