transaction processing (bleurgh)

you should name some data capture mechanisms

optical character recognition: recognises characters

optical mark recognition: recognises marks

barcode scanners: scan barcode

what is electronic data interchange?

The computer-to-computer exchange of documents (done electronically in a special, standardised way using software. 

what does acid stand for?

atomicity, consistency, isolation, durability

what is atomicity?

transactions must be processed entirely or not at all; they cannot be partly processed 

what is consistency?

Referential integrity is upheld and no transaction can violate the defined validation rules (the rules are the same for all transactions) 

what is isolation?

Concurrent processing of transactions should lead to the same result as if the transactions were processed one at a time 

what is durability

• Once a transaction has been processed, it will remain processed, even in a power cut 

• As each part of a transaction is completed, it is held in a buffer on disk until the entire transaction is completed, then the changes to the database will be made 

what is record locking?

Prevents simultaneous access to objects in a database to prevent updates being lost or inconsistencies in the data arising 

how does record locking cause deadlock?

If one user is making a transfer from customer A's account to B's account and another user is making a transfer from B's account to A's account, both accounts will be locked due to record locking, and neither transaction will proceed. 

what is serialisation

serialisation ensures that transactions do not overlap in time and cannot interfere with each other (to avoid updates being lost)

what is commitment ordering?

• Transactions are ordered in terms of their dependencies on each other as well as the time they were initiated 

• One request can be blocked until the other is completed 

what is timestamp ordering?

• each object in the database has a read and write timestamp 

• The timestamps are updated whenever an object is read or written 

• When a user wants to save an update, the current read timestamp is compared to what it was when they started the transaction and if it's not the same, the DBMS knows another user has accessed the same object