Database Reference
In-Depth Information
•
Access to system data can be controlled through object privileges
to base tables, logical views and object privileges to them, or
intricate database design.
•
A materialized view is a database view that stores both definition
and the result of the related sub-query. It therefore qualifies as
a snapshot relation. You can create, alter and drop materialized
views via the
Create-Materialized-View
statement, the
Alter-
Materialized-View
statement and the
Drop-Materialized-View
statement respectively.
Logical views constitute a very important part of a database, providing a number of
conveniences that translate to improved efficiency, flexibility and productivity. As you
will see in the upcoming chapter, they also form an integral part of the database
system catalog.
13.5 Review Questions
1.
What is a logical view? Discuss the importance and usefulness
of logical views in a database.
2.
When are views updateable and when are they not? Discuss.
3.
Practice writing SQL statements to define logical views for
various scenarios. Use the sample college database as your
model.
4.
Briefly explain the three levels of security in a typical database
system. Explain how Oracle's implementation of SQL
facilitates these three levels.
5.
Improve on your college database (from chapter 11) by doing
the following:
a.
Create a user profile called
EndUser,
for your database.
Create a second profile called
Developer
.
b.
Create two roles: one for each profile (you may call
them
EndUserR
and
DeveloperR
respectively). Grant
appropriate system privileges to these roles.
c.
Create two users:
BruceEnd
and
BruceDev. BruceEnd
must belong to profile
EndUser
, with default role
EndUserR
;
BruceDev
must belong to profile
Developer
,
with default role
DeveloperR
. Both users must have your
tablespace (created from chapter 11) as their default
tablespace, with QUOTA UNLIMITED.
