Summary

Good database design ensures a longer-living and more efficient database system. By spending the time to design it carefully, designers can avoid most of the commonly repeated errors that plague many existing databases.

The database lifecycle (DBLC) can be defined in many ways, but it comes down to the same main steps. First, the Analysis phase is where information is gathered and the existing system is examined to identify current problems, possible solutions, and so on. Then, the Design phase is where the new system is carefully designed, first conceptually for the stakeholders and then logically and physically for implementation. Next, the Implementation phase physically rolls out the database, before the Testing phase brings any problems to light. Then, when the Testing phase has succeeded, the system is put into operation for day-to-day use. Almost immediately, the Maintenance phase starts. As change requests come in, routine optimizations and backups need to be performed. Finally, once maintenance becomes too intensive, a new database cycle begins to replace the aging system.

Transactions ensure that the database remains in a consistent state throughout its existence. There are four principles that keep this so. Atomicity states that all requests within a transaction succeed or fail as one. Consistency ensures that the database will always return to a coherent state between transactions. Isolation ensures that all requests from one transaction are completed before the next transaction that affects the same data is allowed to begin processing. And durability keeps the database consistent even in the case of failures.