Chapter 20 - Transaction processing

» Smart card readers » Barcode readers » Scanners

» Forms » Questionnaires

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

» Electronic Data interchange

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

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

» Using SQL

» Defined as a transaction

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

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

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

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

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

» 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

» 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

» 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

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

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

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

» Timestamp ordering » Commitment ordering

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

» 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?

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

» 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