One creates a database by first modeling the data domain using an entity-relationship (E-R) diagram.
The E-R diagram identifies the entities, the attributes of the entities, and the relationships between entities the
database will track. One then converts the E-R diagram directly to tables and relationships in a database system,
using a set of rules for translation.
CHAP. 8] DATABASE 165
The structured query language (SQL) is the industry-standard language for creating database structures and
manipulating data in a database. SQL can be used interactively, or it can be embedded in programs that access
the database.
Built-in controls help to insure that the data remain consistent and valid. These controls are called referential
integrity constraints. In addition to, or instead of, the standard constraints, a database designer can implement
different controls using triggers. Triggers are stored programs that become active when some data element of
the database changes.
Transactions group related database commands together in order to insure database consistency. If all the
actions in the transaction are successful, the transaction will be committed and the changes made permanent,
but if any action fails, the transaction will be rolled back, and the database restored to the state it was in at the
beginning of the transaction.
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