Computing Science: Databases
Computing Science
Level - National 4 / 5
Databases
Revised May 2012
St Andrew’s High School
Computing Science
Slide 1
Computing Science: Databases
What is a Database
• A database is a structured collection of similar
information on one topic.
• Examples:
– Phone book, library catalogue, criminal records,
dictionary
• A database can be ordered either in ascending (A
to Z) or descending (Z to A) order and on one or
more fields.
• Example:
– A phone book can be sorted by last name and
first name in ascending order (A to Z)
Revised May 2012
St Andrew’s High School
Computing Science
Slide 2
Computing Science: Databases
Important Elements
• A database contains 3 important
elements:
– Fields
– Records
– Files
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Computing Science
Slide 3
Computing Science: Databases
Field
•
A field holds one piece of information
Example:
Forename
Date of Birth
Town
Revised May 2012
Helen
12/12/95
Coatbridge
St Andrew’s High School
Computing Science
Slide 4
Computing Science: Databases
Record
•
A record is a collection of fields
on one person or thing.
Example:
Your record in school would contain:
your name;
date of birth;
your address.
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St Andrew’s High School
Computing Science
Slide 5
Computing Science: Databases
File
• A file is a collection of records on the
same topic.
Examples:
- The Police National Computer
- Customer records in a bank
- Pupil files held on school computers
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Computing Science
Slide 6
Computing Science: Databases
Create and Add Records
• Firstly the basic record structure is created by
deciding on the fields names and field types.
• Secondly you must add new records
– You can add records through a form or just
entering data straight to the table
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Computing Science
Slide 7
Computing Science: Databases
Alter Records
• Once you have created your database, you must
ensure the data is correct.
• You can alter the records through a form, or
through the table.
• You can also alter the record format.
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Computing Science
Slide 8
Computing Science: Databases
Field
• A field is one single piece of information
Example:
- “name”, is one field this would be a text field.
- “date of birth”, is another field and this would
be a date field.
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Computing Science
Slide 9
Computing Science: Databases
Types of Fields
Text
holds letters, numbers and symbols
Numeric
hold numbers for calculations
Date
holds a date
Time
holds a time
Graphic
holds a picture
Calculated field
performs a calculation on the
contents of one or more fields
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St Andrew’s High School
Computing Science
Slide 10
Computing Science: Databases
Types of Fields (contd.)
Link
Stores a reference to an external media
file or a connection to a related
database table
Boolean
Only allows one of two values:
yes/no
true/false
male/female
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St Andrew’s High School
Computing Science
Slide 11
Computing Science: Databases
Field Validation
Validation ensures data entered is allowable and sensible
Range check:-
Ensures the data entered in the field is
between a lower and upper limit:
e.g.
Cost > £0
AND < £100
Time > 1 min AND < 5 mins
Length check:-
Ensures that the data entered in the field
has a restricted number of characters:
e.g.
PIN
=
4 chars
Password
>=
6 chars
Comments
<
200 chars
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Computing Science
Slide 12
Computing Science: Databases
Field Validation (cont’d)
Restricted
choice
Gives the user a list of options to choose
from. Prevents the user from typing in
errors.
e.g. Available dress sizes 8, 10, 12, 14, 16.
Presence check
Ensures that the field is not left blank.
Unique check
Ensures that the data entered in the field
is different from any other record.
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Computing Science
Slide 13
Computing Science: Databases
Creating a new Field
• Fields can be added
at any time.
• When on the table
view, select the
design view option
• This view will allow
you to enter a new
field.
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Computing Science
Slide 14
Computing Science: Databases
Searching
The search facility allows you to look for
information in the database.
A search may be:
Simple
Look for records with a match on one field
( They have one thing in common.)
Eg Hair = “Brown”
Complex
Look for records with a match on more
than one item in one or more fields.
Eg Hair = “Brown”
AND
Eyes = “Blue”
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St Andrew’s High School
Computing Science
Slide 15
Computing Science: Databases
Comparison operators
<
< =
=
> =
>
< >
Less than
Less than or equal to
Equal to
Equal to or greater than
Greater than
Not equal to
Contains
Eg. To find all records for 1st to 3rd year in a school
database you could search for:
Year <= 3
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Computing Science
Slide 16
Computing Science: Databases
Sorting
Sorting allows you to arrange the records in a
database in alphabetic or numeric order. This can
be ascending
(A to Z or 1 to 9) or descending (Z to A or 9 to 1)
Sorting on More than one field
When two items are the same in one field they can
be separated using a second field for sorting.
For example, it is common to sort lists of names
first by surname and then by first name
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St Andrew’s High School
Computing Science
Slide 17
Computing Science: Databases
Question Time
Complete the questions below from the Standard Grade
Computing J Walsh book chapter 4, pages 63 and 64.
NAT 4:
Foundation KU 1-3 and PS 1-5
General KU 1-3 and PS 1
OR
NAT 4:
Complete the booklet Exercise 1 - 4
NAT 5:
Complete the booklet Exercise 5
Finish the questions above for next day.
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St Andrew’s High School
Computing Science
Slide 18
Computing Science: Databases
Calculated Field/ Computed Field
A calculated field allows you to carry out a calculation on
another field or fields and return the answer in the
calculated field (similar to formulae in a spreadsheet).
Example:
Field 1: Date of birth
Field 2: Today's date
Field 3: Age
Field 3 is a calculated field and contains the
formula: Today’s date - Date of birth
Other examples of calculated fields often used in reports
include totals and sub-totals.
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Computing Science
Slide 19
Computing Science: Databases
Report
Any information on your database that you print
out is a report. You would normally do a search and
/ or a sort, and then select which fields you want to
print.
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Computing Science
Slide 20
Computing Science: Databases
Size of a field
This is the total number of characters, including
spaces, needed to hold the information in a field.
Eg. A Field containing the
data ‘Computing
Department’
Would have a field size of
20.
Revised May 2012
Examples of databases
include:Telephone directory
Police National Computer
A personal Christmas card
list.
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Computing Science
Slide 21
Computing Science: Databases
Calculating the storage requirements of a database
file
Field
Size of field
1
2
3
4
5
6
7
8
30
4
25
24
8
4
4
8
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Computing Science
Slide 22
Computing Science: Databases
Field
Size
1
2
3
4
5
6
7
8
Bytes
30
4
25
24
8
4
4
8
required
30
4
25
24
8
4
4
8
Total for one record= 107 bytes
If a database has 50 records the storage space
required=
107 X 50 = 5350 bytes
5350 / 1024 = 5.22 Kilobytes
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Computing Science
Slide 23
Computing Science: Databases
Keywords
This is the text used to search a file for a particular entry.
Key Field
This is a field which contains unique information for each
record. That is, each record has a different number or text
in the key field. Doing a search for an item on a unique field
will only give one record.
Example: SQA has a database of all pupils attempting
Standard Grade Exam. Each pupil has a unique candidate
number because there will be more than one pupil with the
same name and date of birth.
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St Andrew’s High School
Computing Science
Slide 24
Computing Science: Databases
Types of Database
Flat File
database
Used to store information about one
topic
Relational or
Linked Database
Used to store information about several
related topics.
Each topic stored as a separate file or
table.
Database tables linked to create one
large database.
The tables are linked through a key
field, referred to as a primary key in
one table and a foreign key in the other
table.
e.g. Pupils database
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Computing Science
Slide 25
Computing Science: Databases
Linked/Relational Database Example
Pupils Database
Pupils table
Registration Classes table
Forename
Surname
Date of Birth
Registration Class
Room
Registration teacher
Room phone number
Registration Class
The two tables are linked by the same field being in both tables.
This must be a key field in one of the tables.
Registration Class is the key field in the Registration Classes table
because it uniquely identifies a single class. This is also referred
to as the primary key.
The Registration Class field in the Pupils table is regarded as the
St Andrew’s High School
foreign
key.
Slide 26
Revised May 2012
Computing Science
Computing Science: Databases
Data Protection Act
Definitions:
Data User
is a person who holds and uses
personal data about others or
controls the use of it.
Data Subject
is a person about whom personal
data is stored by a data user.
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Computing Science
Slide 27
Computing Science: Databases
The Data subjects have the following rights:
•
•
•
•
to know if data is held about them on a
computer
to see a copy of this personal data
to make corrections if necessary
to ask for compensation if data is inaccurate
or access given to an unauthorised person.
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St Andrew’s High School
Computing Science
Slide 28
Computing Science: Databases
Under the Data Protection Act (1984) data
users must:
• get and process the information fairly and
lawfully
• register what reason they hold it for
• hold only relevant information
• hold only accurate and up to date
information
• not keep information any longer than needed
• give individuals access to information about
themselves and, where necessary, correct or
remove wrong information
• take appropriate security measures.
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Computing Science
Slide 29
Computing Science: Databases
Exceptions to the Act
There are exceptions to people’s right to see data
held about them. The public are denied access to
data held by the Police or security forces.
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Computing Science
Slide 30
Computing Science: Databases
Misuse of Computers
The Computer Misuse Act is intended to
protect all types of information (not just
personal) stored on computer systems.
Hacking
This is the act of trying to gain unauthorised
entry to files. This is done by using a wide area
network and passwords.
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Computing Science
Slide 31
Computing Science: Databases
Viruses
Some people enjoy writing and distributing
computer viruses which destroy data and cause
computers to crash or take up processor time
in meaningless calculations. Viruses are usually
spread by copying files (from unofficial
sources).
To prevent viruses spreading:
•
Don’t share disks.
•
Don’t copy software.
•
Use an anti-virus program to check disks
regularly.
Revised May 2012
St Andrew’s High School
Computing Science
Slide 32
Computing Science: Databases
Mail Merge
A database is the second general purpose package
(along with a word processor) required to produce
a mail merged document. Having studied both
these packages, we are now in a better position to
understand how a mail merge works.
Mail merging is the process of combining details
from a database with a standard letter in a word
processing package, to produce personalised
letters - as many letters as there are records in
the database.
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St Andrew’s High School
Computing Science
Slide 33
Computing Science: Databases
Database
Name
Flossie
Year
S1
Name
Josie
Year
S5
Name
Phyllis
Year
S4
Word Processed Standard
Letter
Dear Parent,
I am pleased to inform you that
your child ___________ has
won a prize for the best
Computing student in
__________ Head Teacher.
Having created your database and your standard
letter, you are ready to combine the two, filling the
gaps in the standard letter with information from the
database.
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Computing Science
Slide 34
Computing Science: Databases
Word Processed
Standard Letter with
database fields inserted
ready for mail merge.
Dear Parent,
The database field names are
used to mark where in the
standard letter information
from the database will be
inserted. These are shown in
brackets like so << >> to mark
them.
I am pleased to inform you that
your child <<Name>> has won
a prize for the best Computing When the mail merge is
performed the field names in
student in <<Year>>
brackets are replaced with the
Head Teacher.
appropriate fields from the
database. This is done for every
record in the database.
Revised May 2012
St Andrew’s High School
Computing Science
Slide 35
Computing Science: Databases
Question Time
Complete the questions below from the Standard Grade Computing
J Walsh book chapter 4, pages 63 and 64.
NAT 4 and 5:
Credit KU 1 and PS 1-2
and
Exercise 6 and 7 from the Database Booklet
NAT 5:
Exercise 8 from the Database Booklet
Complete questions for next day.
Copy key points into your jotter.
Revised May 2012
St Andrew’s High School
Computing Science
Slide 36