A Database Trigger is procedure (set of SQL and PL/SQL statements) that is automatically executed as a result of an insert in,update to, or delete from a table.
Rollback Segments are used :
To generate read consistent database information during database recovery to rollback uncommitted transactions for users
A Procedure consist of a set of SQL and PL/SQL statements that are grouped together as a unit to solve a specific problem or perform a set of related tasks.
Procedure is pl/sql subprogram that can accept parameters and can be invoked form calling enviourment.Procedures are created to perform actions on an applications
ORACLE database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.
Oracle database consists of logical storage place which is called as blocks and the bytes in a block is set through DB_BLOCK parameter in parameter file
A declarative integrity constraint is a statement about the database that is always true. A constraint applies to existing data in the table and any statement that manipulates the table. A trigger does not apply to data loaded before the definition of the trigger, therefore, it does not guarantee all data in a table conforms to the rules established by an associated trigger. A trigger can be used to enforce transitional constraints where as a declarative integrity constraint cannot be used.