1. 3.2.3 Data types and data structures
OCR AS Level F452: Data types and data structures
3.2.3 Data types and data structures
c. explain the advantages and disadvantages of different data types and data structures for solving a given problem;
d. design and implement a record format;
e. define different modes of file access: serial, sequential, indexed sequential and random; and justify a suitable mode of file access for a given example;
f. store, retrieve and search for data in files;
g. estimate the size of a file from its structure and the number of records;
h. use the facilities of a procedural language to perform file operations (opening, reading, writing, updating, inserting, appending and closing) on files of different access modes as appropriate.

2. OCR AS Level F452: 3.2.3 Data types and data structures
c. explain the advantages and disadvantages of different data types and data structures for solving a given problem;

3. Selecting suitable data types
OCR AS Level F452: Data types and data structures
Selecting suitable data types
An online bingo company uses the following variables:
Player name
Amount won
Average score
Phone number
What data type should each variable be and why?

4. d. design and implement a record format;
OCR AS Level F452: Data types and data structures
d. design and implement a record format;

5. Record formats Field Name Data Type Maximum size in bytes CustomerID
OCR AS Level F452: Data types and data structures
Record formats
Field Name
Data Type
Maximum size in bytes
CustomerID
String 6
First name 10
Gender
Char 1
Age
Integer 2
A record is just a data structure that allows items of data of different types to be stored together in a single file. Data is stored in different fields.

6. OCR AS Level F452: 3.2.3 Data types and data structures
e. define different modes of file access: serial, sequential, indexed sequential and random; and justify a suitable mode of file access for a given example;

7. OCR AS Level F452: 3.2.3 Data types and data structures
Serial files
In serial files records are stored in the order in which they were entered.
New records are always added at the end of the file. These files are only searchable by going through each record 1 by 1 from beginning to end (serial search).
First name
Surname
Age
David
King 12
George
Smith 34
Matt
Jones 56
Joe
Apple 7
Sarah
Brain 89
Last record entered
First record entered.

8. OCR AS Level F452: 3.2.3 Data types and data structures
Sequential files
In sequential files records are stored sequentially according to some key field, for example alphabetically.
First name
Surname
Age
Joe
Apple 7
Sarah
Brain 89
Lucy
Charles 13
Sam
Charleston 24
Matt
Jones 56
David
King 12
Craig
Pendlby 57
George
Smith 34
Files stored sequentially by surname.

9. Indexed sequential files
OCR AS Level F452: Data types and data structures
Indexed sequential files
In indexed sequential files records are stored according to some key field and one or more indexes are used to make searching even more efficient.
Index
Sequential File
First name
Surname
Age
Joe
Apple 7
Sarah
Brain 89
Lucy
Charles 13
Sam
Charleston 24
Matt
Jones 56
David
King 12
Craig
Pendlby 57
George
Smith 34
Letter
Index A 1 B 2 C 3 J 5 K 6 P 7 S 8

10. OCR AS Level F452: 3.2.3 Data types and data structures
Random files
Are files in which records have been placed in the file according to a mathematical hash algorithm.
For example by generating a position based on a combination of the customers initials and DOB.
These are fast to search because to find a record you just repeat the hash algorithm.

11. Advantages & disadvantages of file types
OCR AS Level F452: Data types and data structures
Advantages & disadvantages of file types
Advantages
Disadvantages
Serial
Items stored in
any order
Take a long time to search.
Sequential
Items stored in a set order so they are faster to search.
Inserting new items is more complicated.
Indexed Sequential
Very fast to find items.
Every time an item is inserted the index needs updating.
Random
The fastest to search.
Most complicated to implement.

12. f. store, retrieve and search for data in files;
OCR AS Level F452: Data types and data structures
f. store, retrieve and search for data in files;

13. OPEN READ WRITE INSERT APPEND CLOSE
OCR AS Level F452: Data types and data structures
Common file operations
playerName = “Dave”
playerScore = “500”
OPEN playerscores.txt
count = 0
while count<numLines(playerscores.txt)
READ line(count)
IF line(count) = playerName
WRITE currentScore
CLOSE playerscores.txt
ELSE
count=count+1
CLOSE playerscore.txt
OPEN
READ
WRITE
INSERT
APPEND
CLOSE
You dont need to be able to do this in any particular language as long as you know what these basic commands do.

14. OCR AS Level F452: 3.2.3 Data types and data structures
g. estimate the size of a file from its structure and the number of records;

15. Estimating the file size of records
OCR AS Level F452: Data types and data structures
Estimating the file size of records
Field Name
Data Type
Maximum size in bytes
CustomerID
String 6
First name 10
Gender
Char 1
Age
Integer 2
So if this file had 10 records in it it’s size would be, to get the size of one record (19), then 19*10 for the size of all records together (190), then to give some margin for error. So the estimated file size would be 209.
Work out the size of each field
Add together the size of each field to get the size of one record.
Multiply by the number of records.
Add 10%

16. OCR AS Level F452: 3.2.3 Data types and data structures
h. use the facilities of a procedural language to perform file operations (opening, reading, writing, updating, inserting, appending and closing) on files of different access modes as appropriate.;