Editing Atomicity (database systems) (section)

{{short description|Property of the ACID database system}}
{{More citations needed|date=April 2020}}
In [[database system]]s, '''atomicity''' ({{IPAc-en|ˌ|æ|t|ə|ˈ|m|ɪ|s|ə|t|i}}; from {{langx|grc|ἄτομος|átomos|undividable}}) is one of the [[ACID]] (''Atomicity, Consistency, [[Isolation (database systems)|Isolation]], [[Durability (database systems)|Durability]]'') transaction properties. An '''atomic transaction''' is an ''indivisible'' and ''[[Irreducibility|irreducible]]'' series of database operations such that either ''all'' occur, or ''none'' occur.<ref>{{cite web
| access-date = 2011-03-23
| publisher = Webopedia
| title = atomic operation
| date = 25 November 2003
| quote = An operation during which a processor can simultaneously read a location and write it in the same bus operation. This prevents any other processor or I/O device from writing or reading memory until the operation is complete.
| url = http://www.webopedia.com/TERM/A/atomic_operation.html}}</ref> A guarantee of atomicity prevents partial database updates from occurring, because they can cause greater problems than rejecting the whole series outright. As a consequence, the transaction cannot be observed to be in progress by another database client. At one moment in time, it has not yet happened, and at the next it has already occurred in whole (or nothing happened if the transaction was cancelled in progress).

An example of an atomic transaction is a monetary transfer from bank account A to account B. It consists of two operations, withdrawing the money from account A and saving it to account B. Performing these operations in an atomic transaction ensures that the database remains in a [[Data consistency|consistent state]], that is, money is neither lost nor created if either of those two operations fails.<ref>{{cite web
| url = http://archive.oreilly.com/pub/a/onjava/2001/11/07/atomic.html
| url-status = dead
| archive-url = https://web.archive.org/web/20160303090517/http://archive.oreilly.com/pub/a/onjava/2001/11/07/atomic.html
| archive-date = 2016-03-03
| title = Atomic File Transactions, Part 1
| last = Amsterdam
| first = Jonathan
| website = O'Reilly
| access-date = 2016-02-28
}}</ref>

The same term is also used in the definition of First normal form in database systems, where it instead refers to the concept that the values for fields may not consist of multiple smaller values to be decomposed, such as a string into which multiple names, numbers, dates, or other types may be packed.