|In order to
understand why CICS is necessary, you must understand what a transaction
is. The definition presented in the
article by Comaford is quite common and is known as is ACID definition. ACID stands for Atomic, Consistent,
Isolated, Durable. [Comaford]
|Atomic means that a
transaction will operate on one or more tables and rows such that either all
of the changes occur or none of the changes occur. This group
is known as a unit of work (UOW). A Commit occurs when all of the
changes succeed and the changes are made permanent. A Rollback occurs to reverse the changes
and the database is restored to how it was before the start of the UOW.
that the database conforms to all of its rules at the end of any work. For example, this might mean that no two
row identifiers are the same.
|Isolated means that
changes performed by one person cannot be seen or interfere with anyone else
until they are committed. It is as though you have your own private database.
|Durable means that
once changes to the database are committed, the change can live through a
system failure. Uncommitted changes
cannot survive a system failure. [Nusphere]