Unit 10

Question 1

Entity

Answer 1

An object, person, event or thing of interest to an organisation and about which data are recorded.

Question 2

Attribute

Answer 2

A property or characteristic of an entity; Attributes are the columns or fields in a table

Question 3

entity relation

Answer 3

one to one, one to many, many to many

Question 4

1st Normal Form

Answer 4

There are no repeating groups
All the key attributes are defined
All attributes are dependent on the primary key

Question 5

2nd Normal Form

Answer 5

It’s already in first normal form
It includes no partial dependencies (where an attribute is dependent on only part of the key)

Question 6

3rd Normal Form

Answer 6

It’s already in second normal form
It includes no transitive dependencies (where a non-key attribute is dependent on another non-key attribute)

Question 7

Internal Level

Answer 7

The view of the entire database as it is stored
This is the level where the data is organised and indexed
It is normally hidden from the users by the DBMS

Question 8

Conceptual level

Answer 8

Gives a single, usable view of all the data on the database
Used mainly by the database managers and administrators

Question 9

External view

Answer 9

Data is arranged into different views to suit different users requirements and access rights

Question 10

SQL queries

Answer 10

SELECT
INSERT (same as INSERT INTO)
UPDATE
DELETE
FROM
WHERE
ORDER BY
CREATE TABLE

Question 11

Record Locks

Answer 11

Prevent simultaneous access to objects in database by locking a record while it is in use so other users are denied access to that record. Can result in deadlock if access is requested simultaneously. Can be implemented by storing a flag with each record to indicate if it is currently being accessed

Question 12

Serialisation

Answer 12

Ensures that transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost. Implemented using Timestamp ordering

Question 13

Timestamp ordering

Answer 13

A timestamp is given to each transaction so that if 2 transactions affect the same object (record) the transaction with the earlier timestamp would be applied first and to ensure the updates are not lost. Every object in the database has a read and write timestamp which are updated whenever an object in the database is read or written

Question 14

Commitment Ordering

Answer 14

Serialisation technique so when users are simultaneously accessing the same object in database transactions are ordered in terms of their dependencies on each other and the time they were initiated