Views

Views
Recall from Section 3.4 the definition of a view:
View The dynamic result of one or more relational operations operating on the base
relations to produce another relation. A view is a virtual relation that does not
necessarily exist in the database but can be produced upon request by a
particular user, at the time of request.
To the database user, a view appears just like a real table, with a set of named columns
and rows of data. However, unlike a base table, a view does not necessarily exist in the
database as a stored set of data values. Instead, a view is defined as a query on one or more
base tables or views. The DBMS stores the definition of the view in the database. When
the DBMS encounters a reference to a view, one approach is to look up this definition and
translate the request into an equivalent request against the source tables of the view and
then perform the equivalent request. This merging process, called view resolution, is discussed
in Section 6.4.3. An alternative approach, called view materialization, stores the
view as a temporary table in the database and maintains the currency of the view as the
underlying base tables are updated. We discuss view materialization in Section 6.4.8. First,
we examine how to create and use views.