transaction processing Flashcards
(14 cards)
Automatic data capture form
(MICR)
Cheques paid into the bank are scanned using magnetic ink character recognition
Automatic data capture form
Optical mark recognition (OMR )
scans documents such as lottery tickets, multiple choice questionnaires.
eg: surveys, and assesments
optical character recognition (OCR)
can be used to scan forms
transaction processing
A transaction is defined as a single operation executed on data. However a collection of operations can also sometimes be considered a transaction.
ACID
stands for…
Atomicity, Consistency, Isolation, Durability and is a set of rules all DBMS must use to ensure data integrety
Atomicity:
- All operations in a transaction succeed or fail as a whole
- If any operation fails (eg power cut) , the transaction is rolled back
- Ensures partial transactions do not occur
Consistency:
A transaction must maintain the referential integrity rules between linked tables. EG it would not be possible to record a mark in RESULTS table for a student who is not in the STUDENT table in database
Isolation:
- Transactions are isolated from each other
- Intermediate states are not visible to other transactions
- Prevents conflicts and data inconsistencies
Durability:
- Committed transactions persist even in case of system failures
- Ensures data is not lost once a transaction is complete
Record locking:
technique used in (DBMS) to prevent conflicting access to data by multiple transactions or processes
While one person is editing a record, this ‘locks’ the record so prevents others from accessing the same record.
problems with multi user databases.
multiple users
Allowing multiple users to simultaneously update a database table may cause one of the updates to be lost
When an item is updated, the entire record including the whole block in which the record is physically held) will be copied into the users own local memory area
Serialisation
this is a technique which ensures that transactions do not overlap with each other or lead to updates being lost. A transaction cannot start until the previous transaction is finished. It can be implemented using timestamp ordering
Timestamp ordering
whenever a transaction starts it is given a timestamp, so that if two transactions affect the same object (eg a record or a table) the transaction with the earliest timestamp should be applied first
Commitment ordering
used to ensure that transactions are not lost when two or more users are simultaneously trying to access the same database object.
