Chapter 20 - Transaction processing

Question 1

What are 3 examples of automated methods?

Answer 1

» Smart card readers
» Barcode readers
» Scanners

Question 2

What are 2 examples of manual methods of data capture?

Answer 2

» Forms
» Questionnaires

Question 3

What are 3 ways in which data can be transferred into a database?

Answer 3

» DMBS software
» Typing it into a customised form
» Using EDI

Question 4

What does EDI stand for?

Answer 4

» Electronic Data interchange

Question 5

What is EDI?

Answer 5

» Is the computer to computer exchange of documents such as purchase orders, invoices and shipping orders

Question 6

What is the main requirement of using EDI, and how does it help the environment?

Answer 6

» Must be in standard format so that the computer can understand it
» It replaces post, email or fax, therefore saving paper

Question 7

How can you select data?

Answer 7

» Using SQL

Question 8

What is a single logical operation?

Answer 8

» Defined as a transaction

Question 9

What is Transaction processing?

Answer 9

» Any information processing that is divided into individual, indivisible operations called transactions

Question 10

What is the base functionality of all relational databse?

Answer 10

» Referred to using the acronym CRUD
» Create - Insert/create
» Read - Select
» Update - Update
» Delete - Delete

Question 11

What does DBMS stand for?

Answer 11

» Database mangement systems
» Provides a layer for the user and the programmer

Question 12

What does ACID stand for, and what is the purpose?

Answer 12

» Atomicity, Consistency, isolation, Durability
» Set of properties to ensure data integrity is maintained as well as transactions are processed reliably

Question 13

What is Atomicity?

Answer 13

» Ensures that a transaction is processed in its entirety or not at all
» Half- completed change must not be saved back to the database

Question 14

What is Consistency?

Answer 14

» Ensures that no transactions can violate any of the defined validation rules
» Referential integrity, will always be upheld - Meaning any change in the databse must retain the overall state of the database

Question 15

What is isolation?

Answer 15

» Ensures that concurrent execution of transactions leads to the same result as if transactions were processed one after the other
» Transactions must not be interrupted by another transaction

Question 16

What is durability?

Answer 16

» Ensures once a transaction has been committed, it will remain so, even in the event of system failure
» DBMS writes the effects of the transactions into secondary storage rather than RAM
» Held in buffer until all elements are compelted
» Only then will the changes to the database tables be made

Question 17

What is the purpose of record locking?

Answer 17

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

Question 18

What is one problem with record locking?

Answer 18

» A dealock can arise where if 2 users are attempting to update 2 records

Question 19

What is Serialisation?

Answer 19

» Ensures that transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost

Question 20

What are the 2 techinques of serialisation?

Answer 20

» Timestamp ordering
» Commitment ordering

Question 21

How does timestamp ordering work?

Answer 21

» If 2 transactions affect the same object, the transaction with the earlier timestamp should be applied first

Question 22

Explain how timestamp ordering works?

Answer 22

» Every object in the database has a read and write timestamp, which is updated whenever an object is read or written
» When the user tries to save an update, if the read timestamp is not the same as it was when they started the transaction, the DMBS knows another user has accessed the same object?

Question 23

What is commitment ordering?

Answer 23

» Another serialisation technique to ensure that no transactions are lost if 2 clients are simultaneously trying to update a record

Question 24

Explain how commitment ordering works?

Answer 24

» Transactions are ordered in terms of their dependencies on one another as well as the time they were initated
» Can be used to prevent deadlock by blocking one request until another is completed

Question 25

What is the purpose of inbuilt redundancy?

Answer 25

» Protects transaction data from system faliure
» Duplicate hardware is located in different geographical areas, mirrors every transaction that takes place
» If this fails, the backup system automatically takes over

Question 26

What is OCR?

Answer 26

» Optical character recognition
» Automatically reads text by interpreting the shape of the letters

Question 27

What is OMR?

Answer 27

» Optical mark recognition
» Reduces human error, mostly used in the lottery industry

Question 28

What is QBE?

Answer 28

» Query by example
» Graphical - making use of visual tables
» User doesn’t need to remember finer details