Week_11?

Question 1

The complexity of a large database is handled by DBMS which provides Three level architecture. What does each level do.

Internal Level
Conceptual Level
Local or External Level

Answer 1

Internal Level: How the data is stored and accessed

Conceptual Level: What data are available in the database

Local or External level: Limited and simplified views of the database suitable for a single application or a group of associated applications

Question 2

3 points a External Schema does:

Answer 2

Several external schemas in a database.

Provides a means of limiting the perceived complexity of a large system

They hide those parts of the database which are not required for a particular purpose(good security)

External schemas are based on the conceptual
schema

Each external schema describes a section of the
database of interest to a particular group of users (or
programs)

Above the external schema are the application
programs called the Application Level.

Question 3

3 points a Conceptual Schema does:

Answer 3

Describes the global view of the database in a logical form

Avoids the need to know the exact physical structure and access method required for the physical data

The conceptual schema also describes the global constraints on the data.

Effectively you are the Database Developer or
Administrator for your own database rather than a
programmer with a limited (External) view of the
database.

Question 4

3 points a Internal Schema does:

Answer 4

Describes a global view of the data in technical terms such as record formats, data compression techniques, pointers, indexes and has tables

Conveniently the conceptual schema describes the global view of the data at a logical level without this technical complexity

Below the Internal Schema is the operating system and the hardware called the physical level.

Question 5

In DBMS what is Data Independence?

Answer 5

Data Independence is the capacity to change the schema at one level of the database without having to change the schema at a higher level.

Two Types: logical and physical

Question 6

What is Logical Data Independence?

Answer 6

The capacity to change the conceptual schema without changing the external schema nor application programs

Examples:
Adding and removing base tables and attributes
Adding and removing constraints on data
Granting and revoking access rights

Question 7

What is Physical data Independence?

Answer 7

The ability to change the internal schema without causing changes to conceptual database design nor to application programs.

Examples:
Changing the file organisation
Using different storage devices for different tables
Modifying indexes or hashing algorithms.

Question 8

Name 3 kinds of Database Security Controls

Answer 8

Authentication:
Determining whether a user is who her or she claims to be

Authorisation:
Granting a right or privilege, which enables a user to legitimately have access and manipulate a table or view.

Accounting:
Monitoring database usage