Download Databases and Database Management Systems

Databases and
Database Management
Systems
Definition
• A database is an application
package used for storage and
retrieval of data
• A database is a structured
collection of related data
Databases and DBMS
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Why Use a Database?
• All organisations need to keep
records of transactions they perform
with suppliers and customers
• Organisations need records of
employees, orders, invoices etc
• The business needs to be able to find
information quickly and easily as
needed
Databases and DBMS
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Terminology
• Entity
– This is the thing/object you are
recording information about.
– Types of entities
•
•
•
•
Person
Country
Product
Order
Employee
Customer
Invoice
Part
Databases and DBMS
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Attributes
• Attributes are the characteristics
that describe the entities. For the
entity Employee:
–
–
–
–
Name
Age
Tel No
Dept
- Address
- Gender
- Soc Sec Number etc
- Date Hired
Databases and DBMS
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Fields
• This is where we store the
attributes
– Name
– Age
– Address etc
• No two fields can have the same
name
Databases and DBMS
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Record
• A record holds all the data relating
to a single person or a single
transaction etc
• A record is a collection of Fields
• The number if Fields needed depends
on the subject
Databases and DBMS
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A File
• Is a collection of records
• All the student records would make
up the Student File
• All the employee’s records could
make up the Employee File
Databases and DBMS
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A Organisation Database
• Contains all the files within the
organisation
• A College Database could contain the
following files
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–
–
–
–
Student File
Course File
Grant File
Personnel File
Student Applications File
Databases and DBMS
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Database Models
• Not all databases store data in the same
way. This depends on the type of
software used.
• Database Models are
– Relational
– Network
- Hierarchical
- Object Oriented
• For our course we are using Access which
is a Relational Model
Databases and DBMS
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DBMS
• The Database Management System
(DBMS) is the software that
manages the database
• It is the user interface that allows
the user to create, add, delete and
generally manipulate the data in the
database
Databases and DBMS
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COLLEGE DATABASE
Databases and DBMS
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COLLEGE DATABASE
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COLLEGE DATABASE
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Linking
• We need to repeat some fields
so that we can LINK the tables
• The repeated fields allow us to
link the information in one table
to that in another
Databases and DBMS
Slide 15
PRIMARY KEY
• A primary key is one that uniquely
identifies a record
• Student ID is a number allocated to
each student as there may be 2
students with the same name
Databases and DBMS
Slide 16
Relationships
• If we want to link data from
different tables we must define
RELATIONSHIPS between the
tables
• This involves linking the Primary
Key field of one table with a field
in a second table
Databases and DBMS
Slide 17
Database Query
• When we want to extract information
from a database this is called a
‘Query’
• The result is a screen display that
shows the information you want
which may have been extracted for
one or more tables
Databases and DBMS
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Features of a DBMS
• It allows us to create database files
• It enables the user to update, delete,
add or change data in the database
• It enables the user to link tables
• It enables the user to query the
database
• The user can produce reports on
screen or in printed form
Databases and DBMS
Slide 19
Query “Co Mayo”
• If we query the
Student database
regarding which
students come from
Co Mayo the
database will give us
the following result
Databases and DBMS
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Advantages of Databases
• The DBMS makes the entry of data
to the system is quick and easy
• Data is organised in a way that
minimises data redundancy (reentering of the same data over and
over)
Databases and DBMS
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Advantages
• A DBMS allows the organisation to
have a central store of information
so anyone who needs access can get
it
• A DBMS can keep data secure by
using passwords etc and limiting
access to the data
• Better access to data for decisionmaking
Databases and DBMS
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Advantages
• Easy update and retrieval of data
• Easy to create reports for
management
• Reduced data redundancy
• Data is shared throughout the
organisation
• Better security of data
• Better data integrity
Databases and DBMS
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Disadvantages
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Cost of the software
Complexity
Size – huge amounts of data
Backup procedures required
High impact of failure
Skilled personnel needed to
maintain a DBMS
Databases and DBMS
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Summary
• A DBMS is a powerful piece of software
for managing data
• Can store large quantities of data
• Data is consistent throughout the
organisation when a DBMS is used (data
integrity)
• It is easier to maintain data security
• It is much easier to distribute information
throughout the organisation
Databases and DBMS
Slide 25