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In database systems, atomicity (or atomicness; from Greek ''a-tomos'', ''undividable'') is one of the ACID transaction properties. In an atomic transaction, a series of database operations either ''all'' occur, or ''nothing'' occurs. The series of operations cannot be divided apart and executed partially from each other, which makes the series of operations "indivisible", hence the name. A guarantee of atomicity prevents updates to the database occurring only partially, which can cause greater problems than rejecting the whole series outright. In other words, atomicity means ''indivisibility'' and ''irreducibility''. 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). The etymology of the phrase originates in the Classical Greek concept of a fundamental and indivisible component; see atom. == Examples == An example of atomicity is ordering an airline ticket where two actions are required: payment, and a seat reservation. The potential passenger must either: # both pay for and reserve a seat; OR # neither pay for nor reserve a seat. The booking system does not consider it acceptable for a customer to pay for a ticket without securing the seat, nor to reserve the seat without payment succeeding. Another example is that if one wants to transfer some amount of money from one account to another, then the user would start a procedure to do it. However, if a failure occurs, then due to atomicity, the amount will either be transferred completely or will not be even initiated. Thus atomicity protects the user from losing money due to a failed transaction. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Atomicity (database systems)」の詳細全文を読む スポンサード リンク
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