2.4

Question 1

File

Answer 1

Set of related records

Question 2

Record

Answer 2

A collection of related fields (treated as one unit for processing)

Question 3

Field

Answer 3

A single data item

Question 4

Fixed Length Record

Answer 4

• Same number of bytes in each record
• Wated memory in the field
• Faster to process
• Easier to program
• May not be enough space in field

Question 5

Variable length Record

Answer 5

• Has a different number bytes in each record
• No wasted memory
• Harder to program
• Slower to process
• Data will not be truncated

Question 6

Master File

Answer 6

A file containing relatively permanent information usually updated periodically

Question 7

Transaction File

Answer 7

Collection of records used in batch processing to update a master file

Question 8

Full Backup: Gererations

Answer 8

• Keep 3 latest Master and Transaction file
• Grandfather - Father - Son
• If one version is corrupted, the previous versions are still available

Question 9

Incremental Backup: Transaction Logs

Answer 9

• Saves storage space and is faster
• Only backs up data that has changed and replaces older backups
• restores database to a point in time
• all log records are required to replay database changes up to that point in time

Question 10

Archiving

Answer 10

The process of freeing up data on a computer system that is no longer in use but is kept for historical/security reasons and is stored securely off site

Question 11

Serial

Answer 11

Records are added to transaction file in the order they are recieved

Question 12

Sequential

Answer 12

• Records are stored in master file in key field order
• Used as records are normally accessed in order to update an entire file

Question 13

Indexed Sequential

Answer 13

• Index allows for data to be accessed directly
• Records are saved in blocks stored sequentially
• Locate records using index block pointers

Question 14

Indexed sequential advantages

Answer 14

• Fast searching using index
• Could be faster than searching overflow area
• Easy to add further records by adding extra data blocks and index pointers

Question 15

Direct Access File: Need for overflow

Answer 15

• Data collision occurs when 2 records are hashed to the same location
• A flag is set adn the latest data is stored in a seperate file called the overflow area

Question 16

Direct Access File: need for organisation

Answer 16

• Data in the overflow area is searched in a linear manner
• When there are many items in the overflow area, access becomes slower
• A new hashing algorithm is required and a larger file may be needed

Question 17

Validation

Answer 17

• A check to ensure that data is sensible and reasonable
• Check against a set of rules setup in a program
• Only proves that data is reasonable, not correct

Question 18

Types of Validation

Answer 18

Range Check
Presence Check
Length Check
Type Check
Format Check
Lookup Check

Question 19

Verification

Answer 19

A check ensuring that data has been copied correctly from one medium to another

Question 20

Double Entry verification

Answer 20

• data is entered twice
• 2 sets of data are compared to check that they match
• If no match, it is rejected

Question 21

Multi Level index

Answer 21

• Main index contains the location of the next index
• could extend to several levels
• last level contains the physical address of the record