WEEK 5

DBMS – database management system

Data

Data is the information in a form suitable for processing by the computer, such as digital representation
of numbers, text, graphic images or sounds.

Database

A database of collection of related information organized for rapid search and retrieval. Database can
contain all types of data from an address list to students’ scores and grades. Ms Access is a database
program that allows you to organize andmanipulates data in many different ways.

Database Management System (DBMS)

A database management system (DBMS) is a collection of programs that enables you to store, modify,
and extract information from a database. There are many different types of database management
systems, ranging from small systems that run on personal computers to huge systems that run
on mainframes.

Examples of Dbms Packages

DBASE

RBASE

ACCESS

DATACOM/DB

DB2

FOXPRO

IDMS

INFOMIX

INGRES

ORACLE

PARADOX

SQL SERVER

SYBASE

SYSTEM 2000

Examples of Database Applications

The following are examples of database applications:

 automated teller machines

 flight reservation systems

 computerized parts inventory systems

A Microsoft Access Interface

File

The collection of data that makes up a computerized database must be stored physically on some
computer storage medium. The Dbms can then retrieve, update, and process this data as needed.

A file is a sequence of records.

Record

A database is a row of data in a database table consisting of a single value from each column of data in
the table. The data in the column of a table are all of the same type of data, while the rows represent a
given.

Field

A field is a data element that is an essential part of a data record. Withoutit, there would be no record in
the database.

Key

This is a field in a record that holds unique data which identifies that record from other records in the
file or database. Examples of keys are Account no. , product code, student’s admission no. etc. as an
identifier, each key value must be unique in each record.

Types of keys in database include the following:

1. Super key

2. Candidate key

3. Composite key

4. Primary key

Tables

A table in a ddatabase, alternatively known as relation, is a two-dimensional structure used to hold

A row in a table is a collection or instance of one thing, such as a student’s one line record or one line
item on an invoice.

Column

A column contains all information of a single type, and the piece of data at the intersection of a row and
a column, a field, is the smallest piece of information that can be retrieved with the database’s query
language.

An example of column/field is the a field record of lastname

EXERCISE

Define The Folowing Terms

1. Database

2. Field/ column

3. Key

Advantages of DBMS

The database management system has promising potential advantages, which are explained below:

1. Controlling Redundancy: By having centralized database, repeated data that are not necessary can be
avoided. It is not possible that all redundancy should be eliminated; however this redundancy can be
controlled.

2. Integrity can be enforced: Integrity of data means that data in database is always accurate, such that
incorrect information cannot be stored in database. In order to maintain the integrity of data, some
integrity constraints are enforced on the database.

3. Inconsistency can be avoided: When the same data is duplicated and changes are made at one site,
which is not propagated to the other site, it gives rise to inconsistency. So, if the redundancy is removed
chances of having inconsistent data is also removed.

4. Data can be shared: A database can be shared by multiple applications in centralized DBMS as
compared to file system, so now applications can be developed to operate against the same stored data.

5. Standards can be enforced : Since DBMS is a central system, so standard can be enforced easily may
be at Company level, Department level, National level or International level.

6. Restricting unauthorized access: When multiple users share a database but access to data and
information in the database will be controlled. For example, only authorized persons are allowed to
access account office data.

7. Providing Backup and Recovery: A DBMS must provide facilities for recovering from hardware or
software failures. The backup and recovery subsystem of the DBMS is responsible for recovery.
Disadvantages of DBMS

The disadvantages of the database approach are summarized as follows:

1. Complexity : the functionality of a good DBMS makes it an extremely complex piece of software.

2. Size : The complexity of the DBMS makes it an extremely large piece of software, occupying many
megabytes of disk space large amounts of memory to run efficiently.

3. Performance: with the DBMS written for many applications rather than just one, some applications
may not run as fast as they used to.

4. Higher impact of a failure: The centralization of resources increases the vulnerability of the system

5. Cost of DBMS: The cost of DBMS varies significantly, depending on the environment and functionality
provided.

6. Additional Hardware costs: The disk storage requirements for the DBMS may necessitate the
purchase of additional storage space or even additional machines.

7. Cost of Conversion: this include; the cost of converting existing applications to new DBMS and
hardware, cost of training staff to use the new systems and cost of specialist staff to help with
conversion and running of the system.