Chapter 16 Data Representation

Question 1

user defined data type

Answer 1

A data type derived from one or more existing datatypes

used to extend the built-in datatypes
programmer’s requirement

3

Question 2

why are user defined data types necessary

Answer 2

no suitable datatype is provided by the language used
if a programmer needs a specific datatype
that meets program requirements

2

Question 3

non-composite datatype

Answer 3

single datatype that does not refer to another datatype
e.g: enumerated, pointer, real, string, char, boolean

Question 4

composite datatype

Answer 4

datatype that refers to other datatypes
data type is constructed from other datatypes
e.g: record, list, set, array, class, queue, linked list, dictionary

Question 5

record

Answer 5

collection of related items which may be of different datatypes

Question 6

list

Answer 6

indexed collection that can contain different datatypes

Question 7

set

Answer 7

supports mathematical operation

Question 8

class

Answer 8

gives properties and methods for an object

Question 9

array

Answer 9

collection of items of the same datatype

Question 10

enumerated datatype

Answer 10

non-composite
defined by a given list of all possible values
in an order

Question 11

pointer datatype

Answer 11

non-composite
used to reference a memory location

Question 12

dereferencing

Answer 12

getting the value in an address

Question 13

record datatype

Answer 13

composite datatype
a collection of multiple datatypes

Question 14

declaring a range

Answer 14

0-89
DECLARE number : 0..89

Question 15

file organization

Answer 15

Refers to the way data is stored in a file

Question 16

serial file organization

Answer 16

• Data is stored in chronological order
• Easy to append data to the end of the file
• Allows the data to be read in order of when they were taken
• No KEY FIELDS need to be added

Question 17

when is serial used

Answer 17

• Suited to batch processing or for backing up data on a magnetic tape
• When chronological order matters
  appending records
• Small file, so easy to search
  when re-organizing as re-sorting is not required
• Typical use is for a bank to record transactions

Question 18

sequential file organization

Answer 18

• A method of file organization in which files are stored with ordered records
• Records are stored in the order of the key fields
• New records are inserted into their correct position

Question 19

when is sequential used

Answer 19

• When there are unique fields, so it can be used for indexing
• When it needs to be sorted in an order
• When multiple records are required from one search of the file. Eg. Family history file where a search could be used for all records with a particular family name

Question 20

random file organization

Answer 20

1. record location is calculated
   using a hashing algorithm on a key field, speed of data access is increased
2. Can be used as lookup file
   if a record cannot be stored
   then subsequent location is searched (closed hash) or an overflow area is searched (open hash - chaining)

Question 21

hashing algorithm

Answer 21

a mathematical function to find a hash key to access data

Question 22

bucketing (closed hashing)

Answer 22

a method to deal with hashing collisions in which another empty space is found

Question 23

chaining (open hashing)

Answer 23

a method to deal with hashing collisions in which linked lists are used to find the location in ROM

Question 24

rehashing (closed hashing)

Answer 24

a method to deal with hashing collisions in which another algorithm is used

Question 25

how is sequential access used

Answer 25

earliest reading/data is accessed first
each successive reading is read
until final reading is accessed

Question 26

floating point representation

Answer 26

representation of real numbers

Question 27

mantissa

Answer 27

the significant digits of floating point number

Question 28

exponent

Answer 28

the power of base 2 (that the mantissa is raised to)

Question 29

normalization

Answer 29

a technique that is used to make your data more accurate

Question 30

random file

Answer 30

can be read/write at the same time
contains a collection of data
normally as records of a fixed length
can be thought of as having a file pointer that can be moved to any location or address of the file
record at that location can then be read or written

Question 31

Direct access file

Answer 31

Direct access can be done in two ways: Use a hashing algorithm OR Use a sequential file with a separate index file

• In direct access, files using hashing, file access involves directly mapping the hashed key to a specific location in the file where the desired data is stored.
• However, in cases of collision where multiple keys hash to the same location, serial searching within that location might be necessary to retrieve the correct data, potentially impacting direct access efficiency.

Question 32

When is direct access file used

Answer 32

• Opt for a direct access file when quick access to specific data by its location or key is essential, offering faster retrieval and modification capabilities
• An example is a system with many users

Question 33

Serial File Deletion

Answer 33

Deleting in a serial file typically involves marking the record as “deleted” without physically removing it to maintain
sequential order

Question 34

Sequential File Deletion

Answer 34

Data is transferred from the old file to a new one until the targeted record for deletion or modification is encountered, after which any changes are made, and the remaining records are then copied to the new file

Question 35

Direct Access File Deletion

Answer 35

Deleting in a direct access file involves marking the specific location as available, allowing it to be reused for new data

Question 36

Text file Versus Binary file (File organization)

Answer 36

Text file

• Text file stores data in a human readable format according to a character code (ASCII, Unicode)

Binary file

• A binary file stores data in a format that the computer can interpret directly as sequences of bytes. The organisation of a binary file is based on the concept of a record.

Question 37

Problems with using floating-point numbers

Answer 37

• Approximation and Rounding Errors: Floating-point numbers involve approximations, and rounding errors can become significant during computations, particularly in repetitive operations. Accumulation of these small errors might lead to inaccuracies in the final result, especially in complex computations or numerical algorithms.
• Limited Range of Numbers: Floating-point representation has a finite range to store numbers, resulting in limitations on both the minimum and maximum values that can be accurately represented. This limitation can lead to underflow errors when representing extremely small numbers, causing loss of precision or inaccuracies in calculations involving very small values

Question 38

Built-In Data Type

Answer 38

Built-in data types are predefined data types provided by a programming languag

Question 39

Enumerated data type Code snippet

Answer 39

Question 40

Pointer data type Code snippet

Answer 40

Question 41

Set Data Type Code snippet- Using set in Python to remove duplicated items in the list.

Answer 41

Question 42

Set Data Type Code snippet- Using set in Python to remove duplicated items in the list.

Answer 42