Triggers
Triggers are a specialized type of a PL/SQL or Java block of code that is executed, or triggered,
when a specified event occurs. The types of events can be DML statements on a table or view, DDL
statements, and even database events such as startup or shutdown. The specified trigger can be
refined to execute on a particular event for a particular user as part of an auditing strategy.
Triggers are extremely useful in a distributed environment to simulate a foreign key relationship
between tables that do not exist in the same database. They are also very useful in implementing
complex integrity rules that cannot be defined using the built-in Oracle constraint types.
More information on how triggers can be used in a robust distributed environment can be
found in Chapter 17.
External File Access
In addition to external tables, there are a number of other ways Oracle can access external files:
From SQL*Plus, either by accessing an external script containing other SQL commands
to be run or by sending the output from a SQL*Plus spool command to a file in the
operating system??™s file system.
Text information can be read or written from a PL/SQL procedure using the UTL_FILE
built-in package; similarly, dbms_output calls within a PL/SQL procedure can generate
text messages and diagnostics that can be captured by another application and saved to
a text file.
External data can be referenced by the BFILE datatype.
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