YEAR 2 CO1 WEEK 4 TRANSACTION PROCESSING Flashcards
What has to happen before data is added to a database?
The data has to be collected/captured in some way.
Manual methods including transcribing data or using OCR/OMR, scanners or barcode readers.
What happens when data has been collected for the database?
One collected can be transfered to a database either,
Automatically using DBMS Software
Typing it in using a customised form
Importing from another type of file.
What should be done when exchanging data to a database?
Validation should occur to ensure data is sensible along with verification to ensure data entered matches the original.
What are some ways of transcribing data?
Electronic Data Interface - translation may be used to make sure any EDI format can be input directly into different company’s database.
JSON (JavaScript Object Notation) - one of most common medium for describing + exchanging text based data.
SOAP - a standardised protocol that sends messages using HTTP or SMPT.
Describe Transaction Processing.
A single logical operation on data is defined as a single transaction.
Database must ensure not possible to complete only part of a transaction.
Describe what ACID is and what It stands for.
ACID is a set of properties that guarantee that transactions are processed reliably.
ATOMICITY
CONSISTENCY
ISOLATION
DURABILITY
What does Atomicity mean in context of transaction processing?
Atomicity ensures that a transaction must be processed in its entirety or not at all.
Transactions should either succeed or fail but never partially.
What does consistency mean in terms of Transaction Processing?
The transaction should only change database according to rules of the database in order to maintain integrity.
When Relational Database created referential Integrity rules specified between links in tables.
Not possible to create or delete a record if related records exist in linked tables.
Eg. Employee can’t be deleted if have salary details in another table.
What does Isolation mean in terms of Transactional Processing?
Ensures concurrent execution of transactions leads to same results as if the transactions were processed one after another.
Eg. Each transaction should not overwrite other transactions that are being processed at the same time.
What does Durability mean in terms of Transaction Processing?
Ensures once a transaction has been committed, it will remain so even in the result of a power outage.
Describe how record locking works?
In its simplest form the record is “locked” when the first user obtains the data and cannot be accessed by any other user until it is “unlocked”.
Describe what is meant by a deadlock?
Where two users try to access a single record at the same time a situation occurs where neither can be processed.
What is meant by serilisation?
When two or more transactions executed concurrently, effect should be the same if had been executed serially I.e one after another.
Ensures transactions do not overlap in time so cannot interfere with eachother or lead to updates being lost.
What is TimeStamp Ordering?
When transaction starts its given a timestamp so if two transactions affect same object earliest timestamp should be applied first.
What is commitment ordering?
Transactions are ordered in terms of their dependencies between one another as well as the time they were initiated. I.e which data will be updated and how it may potentially affect other transactions.
