Acronym
for "Atomicity, Consistency, Isolation, Durability", as understood
in data-management theory (which underlies engineering of
database management systems [DBMS]s).

Accessible introductions to the value of ACID include ones
from
   * the aD crew [http://www.arsdigita.com/books/panda/databases-choosing]
   * [CL] [http://www.linuxworld.com/linuxworld/lw-1999-09/lw-09-aolserver_3.html]

As [Donal Fellows] said in [The comp.lang.tcl newsgroup]:
 The Holy Four Properties of Transactions, which are (IIRC):
  Atomic - it happens or it doesn't
  Consistent - the story doesn't change underneath your feet
  Isolated - other people can't mess you up
  Durable - once you've finished commit, it doesn't go away

 It's a shame there's not three of them, or we could make religious
 jokes.  :^)

'''DGP''': That's not really a good definition of Consistent, even informally.  Better might be: "you can't $#^&#$&^ it up."  Important
thing is that invalid transactions are not permitted.  CL adds:  the issue with consistency most often is that a particular datamanager doesn't support consistency semantically; it's not particularly that extant datamanagers are wont to behave erratically (at least in this regard).  I repeat:  SQL-less datamanagers often are not able to '''express''' "consistency" as powerfully as SQL can.

[[Explain why and how [MetaKit] and [MySQL] don't respect ACIDity.]]

See also the [Acronym collection]

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[Category Database] [Category Acronym]