Countering ACIDity Workflow agents can implement a form of relaxed transaction processing. 4 Relaxed or extended transactions are activities consisting of several tasks, or operations, that do not satisfy one or more of the ACID properties. 5 Atomicity means that either all changes a task causes to a system state happen or none do. Consistency means that a task takes the system from one consistent state to another. Isolation means that a task's intermediate results are not visible to another task.
Durability means that any changes committed by a task persist.
ACID transactions are the staple of traditional databases because they guarantee that only consistent data is stored and that only consistent snapshots of a changing database are viewed. However, implementing ACID transactions makes stringent demands that cannot be met in an open environment, such as the Internet. For example, if the workflow in our figures were modeled as an ACID transaction, we would have to ensure that the user couldn't be told the order was received until after it had been processed or worse, that an order was received only if it was completed. Of course, these are not reasonable behaviors. Moreover, they are impractical, because they require delaying one task until another task, which might not occur until much later, catches up.