Its all about data

1. CHAPTER 3 : DESCRIPTION OF
DATA

2. Chapter Objectives
At the completion of this chapter, you would have
learnt:
 the different types of data;
 the different types of data structures.

3. Introduction
 Data is any collection of numbers, characters or
other symbols that has been coded into a format
that can be input into a computer and processed.
 The main function of a computer program is to
process data to produce information.
That is, to accept data from the user as
input, process the data and
present the information to the user as
output

4. 3.1 Types of Data
There are two fundamental types of data: Numeric
and Non-numeric.
 Numeric(Qualitative)
Numbers used for sums of money, ages,
distances.
For example 0.33, -0.1, 0.5, 2, 50.01, -100, etc.
 Non-Numeric(Quantitative)
Non numbers such as strings of characters.
For example ‘John’, ‘AS1234G’ and ‘2@**556’,
etc.

5. DATA DIAGRAM
Data
Numeric
Non
Numeric
Char String Logical Pointer DatesInteger Real

6. 3.1.1 Numeric
Divided into two main groups: Integer and Real.
 Integer
 Whole numbers used to count things,
example 1, 2, 3,...
 Count discrete objects such as number of
bananas, orange or pencils.
 Precise values.
 The range of integers provided in a
computer system depends on the
hardware/language used.

7.  REAL
 May have a fractional part, example 1.0,
234.66, ...
 Can be positive or negative.
 To measure things like the length of a
piece of string, or the cost of an item in
dollars and cents.
 Generally NOT a precise value.
 Nearest value is according to the method
of storage and type of arithmetic used
(e.g. for rounding off method, 14.385 in
this case will become 14.39 and 14.382
will become 14.38 whereas for truncation
to two decimal places both 14.385 and
14.382 will become 14.38).

8. 3.1.2 Non-Numeric
1. Character strings
Character strings may consist of
Numbers, Alphabets or
Alphanumeric.
To represent such character strings,
quotes (’) are needed. For example
the name JAMES will need to be
quoted as ‘JAMES’.

9. 2. String
 String characters are stored as codes using
the American Standard Code for Information
Interchange (ASCII) or Extended Binary
Coded Decimal Interchange Code (EBCDIC)
code system.
 String operation usually involves comparison,
concatenation or selection to allow
combinations of strings. Thus strings should
have different values also. For example,
‘A’ < ‘Z’,
‘ABC’ > ‘AAA’
‘Alpha’ < ‘Alphabet’ and
lowercase characters > Uppercase
characters

10. 3.Logical / Boolean data
 Consists of 2 values: True or False.
4.Pointers
 which store the address of variables.
5. Dates
 which allow arithmetic operation on
calendar dates.

11. 3.1.3 Identifiers
 All data items used in a program need to
be declared before usage. This means
to state down the name given to each
data item storage cell known as
“identifier”.
An identifier may be numeric or non-
numeric.
The data type that can be contained
in the storage cell will depend on the
declaration of the cell.

12. These storage cells can be a constant storage cell or
variable storage cell.
 Constants
It is a “Read-only” variable which
contains fixed data values that cannot be
changed during the program execution.
 Variables
Their content changes according to the
users input or the processing of the
program during execution.

13. 3.2 Types of Data Structure
 Data items grouped logically together to give
information about an individual.
 For example, an address book is a data structure
containing data items (names, addresses, phone
numbers etc.).
3.2.1 Arrays and Tables
3.2.2 Structured Diagrams
3.2.3 Static vs. Dynamic Data Structure
3.2.4 Files, Records and Fields

14. 3.2.1 Arrays and Tables
 An array is a sequence of consecutive storage
locations having a common name.
 Refer to the contents of the storage cells of each array
element by a “subscript” or “index” which is enclosed
with a square bracket, e.g. [1], [5,3] or [counter].
 Grouping of variables in an array of several elements.
 For example, a one-dimensional array that stored 6
test marks of a student. This array is called
‘StudentFile’.
 StudentFile
76 77 78 56 89 90
0 1 2 3 4 5

15.  The value in each of the box stores a test mark.
 Refer to the contents of the storage cell of each array
element by a “subscript” or “index”. For example, to refer
to the test mark in box number 3, what you will need to
do is to call the array by its name, followed by the
“subscript” or “index” shown below it. In this case, you
can refer to the contents of box number 3 by calling
“StudentFile[3]”.
 A one dimensional array can only hold a student’s test
marks in this case, so if a data structure that is
supposed to be created to store all the test marks of a
class of students, a two dimensional array must be
used.
 A two dimensional array is a table that can store more
information. An example is shown on the next page.

16. A two-dimensional array that stores 6 tests marks of
3 students.
StudentFile
In this case, you can refer to the content of the third box
in the first row by calling “StudentFile[1,3]”.
1 76 77 78 56 89 90
2 76 89 87 47 85 58
3 56 34 78 67 98 76
1 2 3 4 5 6

17. 3.2.2 Structured Diagrams
 To show the grouping and relationship of data items in
a real case in pictorial form, we can use data structure
diagrams.
Characteristics of a Structured Diagram
 Shows how to sub-divide a data item into its parts
using the three data structure constructs.
Three Data Structure Constructs
Simple elements such as address can be represented
with a rectangle box.
1. Sequence Construction
2. Selection Construction
3. Repetition/Iteration Construction
Address

18. Three Data Structure Constructs
 Simple with lower level - To show its contents more
clearly, it is sub-divided into different parts shown at the
lower level in the following diagrams.
Address
Street Name Postal CodeHouse Number
(Sequence
construct)
(Selection
construct)
CAR
SALOON ESTATESPORTS
O O O

19. Note: If one element connected upwards is a selection, all
elements connected up to the same point must be
selections.
Only one selection will be made regardless of the
number of choices.
Example:
(Repetition / Iteration
construct)
Main
Process EndIntro
*

20. Data Structure on an Address Book
FILE
RECORD TRAILERHEADER
*
ADDRESS TELEPHONENAME
INITIALSSURNAME UNIT-CODEAREA CODE
STREET TOWNHOUSE
NAMENUMBER
oo

21. 3.2.3 Static vs. Dynamic Data
Structure
 “STATIC” data structure - the size of the data structure
needed to store information CANNOT change as the
program runs. E.g. array.
 “DYNAMIC” data structure - the size of the data
structure needed to store information CAN change as
the program runs. E.g. linked list.
 Each member of the list essentially forms a record in
the list.
 Each member record is linked to the NEXT LOGICAL
RECORD by means of a special field within the record
called a POINTER.
 The POINTER field contains the address of the next
logical record in the list.
Note: Not all languages have linked lists.

22. Types of linked lists are
 Binary tree
 Ring
Start point

23. 3.2.4Files, Records and Fields
 File
A file is defined as a group of related data
records handled as a logical unit.
For example, the stock master file contains
data records of all stock items in the
warehouse, the payroll master file contains
data records of all employees currently on
the payroll of the organisation.

24.  Record
A record is defined as a group of related
data items called fields, forming a logical unit.
For example, the stock master record may
contain data items like ITEM-CODE,
DESCRIPTION, UNIT-PRICE, QUANTITY-ON-
HAND and so on. These data items make up
the stock master record, and they are called
FIELDS.

25.  Field
A field is a data item forming a subdivision
of a record.
Record
no. 1
Student
Number
Student
Name
Date of
Birth
Sex Exam
Mark
1289
Cindy
Bridges
080471 F 76
1290
Alan Lim 060970 M 80
Record
no. 1
Record
no. 2
File
Fields

26.  Record key
Definition
A record key is defined as a field within a
record that is used as the basis for ordering
the records in a sequential file and also as a
means of direct access.
Examples
STOCK MASTER file arranged in ascending
order of item code which is the record key that
must be unique.
SUPPLIER MASTER field arranged in order of
vendor number, which is the record key.