Data Independence and Database Views

• view 20

three schema architecture

internal level — storage structure

conceptual

external or view level — describe part of the DB of interests to a particular group

views

an unexecuted query that can be run on demand

update applied to a view as if it were a base table, used for any query whenever base table can appear

deleting tuple from view might request update to base table instead of deletion from base table

not all views are updatable

materialized views used to save query time

DBMS determines what new tuples must be inserted, deleted, or modified in materialized view