transaction processing Flashcards
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
Atomicity:
A transaction must be processed in its entirety or not at all in any situation including a power cut or hard disk crashes. It is not possible to process only one part of a transaction.
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:
Simultaneous executions of transactions should lead to the same result as if they were executed one after the other.
A transaction cannot be interrupted by another transaction.
This transaction must occur in isolation so the other users or processes cannot access the database.
Durability:
Once a transaction has been executed it will remain so regardless of the circumstances surrounding it, such as in the event of a power cut.
Record locking:
preventing simultaneous access to records in a database
it is used in order to prevent inconsistencies or a loss of updates.
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
Record locks
preventing simultaneous access to records in a database
it is used in order to prevent inconsistencies or a loss of updates.
While one person is editing a record, this ‘locks’ the record so prevents others from accessing the same record. (read only if someone else is in it)
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.
