How can the quality of a DDBMS ensured ?
Measure of the success with which the system conforms to some authoritative specification of its behavior. When the behavior deviates from that which specified is, this is called failure .
Levels of reliability:
- application dependent
- application independent
The application dependent part refers mainly to the integrity constraints. The application independent part refers mainly to the ensuring ofthe ACID concepts.
Main aspects of reliability:
- correctness : the system works in accordance with the corresponding specifications
Some kind of software testing methods ( ) can be used. There is no appropriate tool to proof the correctness of a complex software system.
- availability : fraction of the time that the system meets its specification
Usually the requirements of the correctness and of the availability can not be met at the same time.
Increasing correctness decreasing availabilityIncreasing availability => decreasing correctness
Correctness oriented applications ( banking, simulations)
Availability oriented applications ( tourist information system)