Software Development Unit 2
Databases
What is a database?
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A collection of data organised in a manner that
allows access, retrieval and use of that data.
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Data is a collection of unprocessed items, which
can include text, numbers, images, audio and
video.
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Information is processed data; it is organised,
meaningful and useful. Information can be in the
form of audio, images and video.
• Computers process data in a database into
information.
• Database software – Database Management System
(DBMS) - users create a computerised database that
allows them to
• add, modify and delete data in a database;
• sort and retrieve data from the database; and
• create forms and reports from the data in the database.
• Databases allow instant access to data and
information.
• Most organisations realise that data is one of their
more valuable assets, because data is used to
generate information.
• To make sure that data is accessible, organisations
must manage and protect its data. It is vital that the
data stored in database software has integrity and is
kept secure.
• Data Integrity
• For a computer to produce correct information, the
data that is entered into a database must have
integrity – data integrity identifies the quality of the
data.
• Data integrity is important because computers and
people use information to make decisions and take
actions.
• Qualities of Valuable Information:
• For information to have value, it should be:
Accurate – error free
Verifiable – can be proven as correct or incorrect
Timely – has an age limit suited to its use
Organised – arranged to suit the needs and requirements
of the decision maker
• Accessible – available when the decision maker needs it
• Useful – has meaning to the person who receives it
• Cost-effective – should give more value than it costs to
produce.
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The 3 main functions of a database are:
1. Data definition
2. Data manipulation
3. Data control
1. Data Definition
An electronic database allows you to define the data
including its:
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Data Type
Format
Storage requirements
Maintenance of Data Integrity
2. Data Manipulation
Allows you to:
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Manipulate data efficiently
Record and retrieve data easily
Search and sort data for particular purposes
Produce effective and timely reports
Update or add new data at any time
3. Data Control
Allows you to
• Control user access to the data
• Query the database for specific information
• Sort and search faster and more accurately
Database Management System
A DBMS is the program that creates the database and can
manipulate the data within it.
• They have no data in them.
• Are used to create the structure that will contain the
data.
• Allows users to create a database to suit their
particular purposes.
Parts Of A Database
• Databases are made up of RECORDS.
• A record is the information about one particular
person or thing. A record is a group of related fields.
• Each record has a similar structure but contains
different data.
• Every record is made up of a number of FIELDS.
• A field is a ‘container’ for a particular item of data.
• The same field on different records contains the
same kind of data.
• Data is entered into each field of a record.
Example:
• Coordinators at PEGS use a database that contains
information about every student -DeltaLink.
• All the information about any one student is a
record.
• Within each record there would be separate fields
for the student’s first name, surname, address, phone
number, photograph, etc.
A database defines each field by a number of
characteristics such as field size and data type.
• Field size defines the maximum number of
characters a field can contain. Eg the Surname field
contains 15 characters and so has a field size of 15.
• Data type specifies the kind of data a field can
contain and how the field is used.
• Common data types are:
Text – letters, numbers or special characters.
Numeric – numbers only.
AutoNumber – automatically assigned unique number.
Currency – dollar and cent amounts.
Date – month, day, year.
Memo – long text entries.
Yes/No (Boolean) – only Yes or No (True/False).
Hyperlink – e-mail address or Web address that links to a
Web page on the Internet or a Document on a network
• Object – photo, audio, video or other documents.
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Relational Databases
• Early database programs were called ‘flat-file’ databases
because all data was stored in one central table.
• These days most commercial database packages store
and handle data using a Relational Database
Management System (RDBMS).
• A relational database is a database that stores data in
tables that consist of rows and columns. Each row
has a primary key and each column (field) has a
unique name.
• A relational database stores data as well as data
relationships. A relationship is a link within the
data. Relationships are set up between tables within
a relational database. To do this, the tables must
have a common column (field).
• The common column (field) is often linked by a
unique ID number that is assigned to each record.
• Relational databases allow for the efficient sharing
of information between different users.
• Tables in a relational database can be linked in a variety
of ways (relationships):
one-to-one
1. A
relationship means that
for each record in the first table, there is exactly one
record in the second table.
Example:
• Each patient has one medical record and
each particular medical record relates to
only one person.
2. The most common relationship is a
many
one-to-
relationship.
• This means that only one record in the first table can be
related to many other records in the second table BUT
any record in the second table only relates to one record
in the first table.
Example
• One student can take out many books from
the library but any one book can only be
taken out by one student at a time.
many-to-many
3. A
relationship means that for
each record in the first table, many records are required
in the second table AND for each record in the second
table, many records are required in the first table.
• Example
• Each student will study many subjects and
each subject will be studied by many
students.
INFO TECH
MATHS
SCIENCE
Database Features
Storing
• Large amounts of data can be stored for later use or
modification. It is generally stored on hard disk and
backed up to prevent loss
Validation
• All database management systems allow for electronic
validation.
• It involves checking, electronically or non-electronically,
the integrity of data to ensure that the input data is
accurate, relevant and complete.
Sorting
• Data may be sorted alphabetically, numerically,
chronologically, or in descending or ascending order.
• A number of different fields can be sorted
simultaneously in priority order.
Searching
• Allows records to be found according to certain criteria
• Search criteria are established which use a field, a
comparison operator eg >, <, =, etc and comparative
data.
Reporting
• By the process of searching, sorting and calculating,
data is manipulated into meaningful information. This
information must be communicated usually in the form
of a hard copy report.
• Reports include a title, a date and meaningful column
headings.
Data Entry Screens
• Also called forms, act as the interface between the user
and the database and allow data to be entered, edited
and displayed.
• Are linked to the individual primary table and new
records are therefore added to the existing data.
Data Privacy & Security
• Privacy is a major concern for those involved with
databases and their use.
• Large organisations use databases to store
confidential information about their clients.
• Data is not indestructible.
• Data can be (by human error, equipment failure
problems with the software or by a catastrophe
eg fire or flood):
• lost
• corrupted and
• damaged or destroyed
• It can also be
• stolen or
• illegally copied.
• For these reasons data security measures are
essential. These measures include:
1. Backing up the data on a regular basis –
making a copy of the entire database.
- Data can be backed up daily, weekly, monthly
or continuously.
2. Attempting to eliminate factors that cause
accidental losses.
3. Preventing unauthorised access to data
which can result in it being stolen, misused
or corrupted eg
• By using passwords to restrict access.
• By allowing different access privileges for
data for different users. This involves
establishing who can enter data, modify
existing data, delete unwanted data, and
view data.