Database Management Systems

I.T. for Management

Chapter 8
Database Management Systems


A database management system (DBMS) is
computer software designed for the purpose of
managing databases.
Typical examples of DBMSs include Oracle, DB2,
Microsoft Access, Microsoft SQL Server, MySQL,
4th Dimension and FileMaker. DBMSs are
typically used by Database administrators in the
creation of Database systems.


A DBMS is a complex set of software programs that
controls the organization, storage and retrieval of data
in a database. A DBMS includes:
1.A modeling language to define the schema(relational
model) of each database hosted in the DBMS, according
to the DBMS data model.
The three most common organizations are the hierarchical,
network and relational models. A database management
system may provide one, two or all three methods. Inverted
lists and other methods are also used. The most suitable
structure depends on the application and on the transaction
rate and the number of inquiries that will be made.


The dominant model in use today is the ad hoc one
embedded in SQL, a corruption of the relational model by
violating several of its fundamental principles. Many DBMSs
also support the Open Database Connectivity API that
supports a standard way for programmers to access the
DBMS.
Data structures (fields, records and files) optimized to deal
with very large amounts of data stored on a permanent data
storage device (which implies very slow access compared to
volatile main memory).


1.A database query language and report writer to allow
users to interactively interrogate the database, analyse its
data and update it according to the users privileges on
data.
It also controls the security of the database.
Data security prevents unauthorised users from viewing or
updating the database. Using passwords, users are allowed
access to the entire database or subsets of it called
subschemas. For example, an employee database can contain
all the data about an individual employee, but one group of
users may be authorized to view only payroll data, while
others are allowed access to only work history and medical
data

1.A transaction mechanism, that ideally would guarantee
the ACID properties, in order to ensure data integrity,
despite concurrent user accesses (concurrency control),
and faults (fault tolerance).
oIt also maintains the integrity of the data in the
database.
The DBMS can maintain the integrity of the database by not
allowing more than one user to update the same record at the
same time. The DBMS can help prevent duplicate records via
unique index constraints; for example, no two customers
with the same customer numbers (key fields) can be entered
into the database. See ACID properties for more information
(Redundancy avoidance).

Relational DBMS
Edgar Codd worked at IBM in San Jose, California, in
one of their offshoot offices that was primarily
involved in the development of hard disk systems. He
was unhappy with the navigational model of the
Codasyl approach, notably the lack of a "search"
facility which was becoming increasingly useful when
the database was stored on disk instead of tape. In
1970, he wrote a number of papers that outlined a new
approach to database construction that eventually
culminated in the groundbreaking A Relational Model
of Data for Large Shared Data Banks.[1]


In this paper, he described a new system for storing
and working with large databases. Instead of
records being stored in some sort of linked list of
free-form records as in Codasyl, Codd's idea was to
use a "table" of fixed-length records. A linked-list
system would be very inefficient when storing
"sparse" databases
Where some of the data for any one record could be left
empty. The relational model solved this by splitting the data
into a series of normalized tables, with optional elements
being moved out of the main table to where they would take
up room only if needed


In the relational model, related records are linked
together with a "key".


For instance, a common use of a database system is to track
information about users, their name, login information,
various addresses and phone numbers. In the navigational
approach all of these data would be placed in a single record,
and unused items would simply not be placed in the
database. In the relational approach, the data would be
normalized into a user table, an address table and a phone
number table (for instance). Records would be created in
these optional tables only if the address or phone numbers
were actually provided

Features
Shared database with concurrency Control:
This means that the DBMS allows many users
to access the data at the same time which is
very essential for on line systems
Application of business rules:
In a situation where many people are
simultaneously updating database ,it is essential
that all users go through same checks &
controls .for example user may access to
particular table for viewing & not updating

Features
Role based access :
The DBMS allow the database administrator to
create user roles whereby he can define to what
each user can do to the database.
Views:
DBMS allows creation of ‘views’ A view is a
query written in SQL which provides a subset of the
database
Transaction control:
One of the main purpose of a DBMS is to help
implement business transaction ……. Cont

Features
Data independence:
With changing business needs it is important that
we are are able to add more columns or change the
properties of a column
Platform independence:
Many DBMS are available for a wide variety of
operating systems& hardware.Thus data can be
migrated from on environment to another since
DBMS allow import & export of database.
Cont……..

Features
Support for various language interface:
Though DBMS use SQL business data processing
requires more complex manipulation & presentation
of reports& user friendly screen Updating the
database are embedded in commonly used
languages such as Cobol, java etc.
Referential integrality:
The DBMS ensures that if record is deleted all
corresponding child records are deleted

Features
Growth :
DBMS are highly sensitive systems DBMS
software such as oracle,Sybase,SQL server etc can
handle very high volumes of data &
transactions.Thus database can span across several
disks,distributed over several database servers
Distributed Database:
DBMS allow users to execute transactions which
access & update information from any location

File & various types of Database

Originally all data on computers was in the form
of flat files.These file were :
Serial files:each record was stored after the other
in a serial order
Sequential files:each record was stored after
another based on some sequence such as customer
code which made it easier to access
Random files:data could be accessed randomly
Index files: Here two file are kept one file
contains data which is any order other file
contains index

Disadvantages of desecrate files

The programmer who develops an application need
to know a lot about files,where it is stored
How it is accessed What Is Structure.
Each programmer writes different
structure,different formats.
Thus there is duplication of same data
In case data is required in sequential order files
have been sorted & used
The flat file system do not offer any
security,Integrity and transaction control

How does the DBMS Store information

A DBMS maintains the following information
Business Data
Meta Data More information about data
Business &integrity rules
User related information
Who are the authorized user
Which tables & columns can they acce
Are they restricted to specific time of d
………..cont

How does the DBMS Store information

When we create a database we have to take holistic
view of all users of the database & there needs
A database consists of schema or layout consisting
of various pieces of information grouped together in
the form of entities.
Apart from master tables we need to define
transaction tables.Transaction tables are those
where transaction information is stored
Once the database is created the transaction has
been created thru application software

Database languages

There are three types of database languages used
Data Definition languages:
A language to define & alter the structure of the
database
Data manipulation language:
A language or set of commands to query,add ,or
delete records in database.
Data control language:
A language which helps to define user rulesto
access data

SQL Data Manipulation commands

SQL Data Manipulation commands
Data manipulation requires four basic functions
Select
Insert
Update
Delete
SQL performs these tasks very efficiently.

Database languages
Typical SQL Commands

create table phone_numbers (
email
varchar(100) not null references
mailing_list, number_type
varchar(15) check (number_type in
('work','home','cell','beeper')),
phone_number varchar(20)

SQL> insert into phone_numbers values
('ogrady@fastbuck.com','work','(800) 555-
1212');

Types of Database

DBMS are of atleast 4 types
Hierarchical DBMS
Network DBMS
Relational DBMS
Object DBMS

Types of Database

Hierarchical DBMS
Store information in the form of a Hierarchy of
records ie parent child formation
Thus a hierarchical structure is created with the
links pointing from parent records to child records.
Network DBMS
Network DMBS overcome some of inflexibilities
of Hierarchical DBMS the data administrator by
allowing pointers ……Cont

Types of Database

Relational Database (RDBMs)
The concept of RDBMS revolutionaries the DBMS
& widely accepted all over
A relational database is a big spreadsheet that
:

several people can update simultaneously.
A request might be "create a table", "insert a row
into a table", "update an existing row in a table",
"give me a report of the information contained in all
the rows in a table that meet the following
criteria...". ……….Cont

Types of Database

Each table in the database is one spreadsheet. You
tell the RDBMS how many columns each row has.
For example, in our mailing list database, the table
has two columns: name and e-mail. Each entry in
the database consists of one row in this table. An
RDBMS is more restrictive than a spreadsheet in
that all the data in one column must be of the same
type, e.g., integer, decimal, character string, or date.
Another difference between a spreadsheet and an
RDBMS is that the rows in an RDBMS are not
ordered.

Types of Database

Entities & Tuples
Each table represents information which is related
to the entity such as employee
All data related to an entity (employee) is stored
in one row also known as Tuples in RDBMS
The unique identifier for an entity (employee code )
Is known as primary key
The primary key uniquely identifies a row in a
database

Types of Database

Advantages of Relational Database (RDBMs)
Conceptually simple mathematically rigorous
Very flexible since We can query on any column
The database can grow very easily since any number
of records can be added to a table.
The database is very expandable since we can add
columns to existing table
As a result databases like Oracle,Sybase,SQL server
have become very popular

Types of Database
Object DBMS

The success of DBMS system depends upon its
ability to represent the data which is very close
To that in real life
For instance if there is a column containing
information about temperature in degrees
centigrade ,it will be helpful if it is converted in
Fahrenheit along with the column in the metadata
DBMS allow such features are known as object
DBMS


End of Chapter 8

Database Management Systems

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Database Management Systems