  Although ACID is the previous golden rule for transaction support, durability
is now not a basic requirement for data storage. Rather, high availability is
becoming the first-class property required by online applications. We show that
high availability of data is almost surely a stronger property than durability.
We thus propose ACIA (Atomicity, Consistency, Isolation, Availability) as the
new standard for transaction support. Essentially, the shift from ACID to ACIA
is due to the change of assumed conditions for data management. Four major
condition changes exist. With ACIA transactions, more diverse requirements can
be flexibly supported for applications through the specification of consistency
levels, isolation levels and fault tolerance levels. Clarifying the ACIA
properties enables the exploitation of techniques used for ACID transactions,
as well as bringing about new challenges for research.
