Fundamentals of Databases

Question 1

Define Data Model

Answer 1

An abstract model of which things to store and what information about them should be recorded

Question 2

Define Attribute

Answer 2

A characteristic of an entity

Question 3

Define Entity

Answer 3

A thing about which data is to be stored

Question 4

What name is given to an attribute which can uniquely identify each attribute in a table?

Answer 4

Entity identifier/primary key

Question 5

Why are databases normalised?

Answer 5

So they can be efficient without any compromise to the integrity of their data.

-Ensures entities contain no redundant or repeated data.

-Reduces update, deletion and insertion anomalies

-Allows for faster searching and sorting.

-Easier to maintain.

Question 6

What is a Composite (Primary) Key?

Answer 6

A primary key formed from two or more other keys.

Question 7

What name is given to the new table when forming a many-to-many relationship?

Answer 7

A link table

Question 8

What is the role of a Client Server Database?

Answer 8

To provide simultaneous access to a database for multiple clients.

Question 9

What problem occurs when different users attempt to access the same field in a client server database simultaneously?

Answer 9

Concurrent access

Question 10

Name three ways of managing concurrent access;

Answer 10

-Record Locks
-Serialisation
-Timestamp Ordering
-Commitment Ordering

Question 11

What is Normalisation?

Answer 11

The formal process of optimally designing data tables by reducing data redundancy and repetition by converting them into normal forms.

Question 12

What is 1st Normal Form?

Answer 12

There are no repeating attributes. All the data in the database is atomic (meaning that no single column contains more than one value, cannot be split down any further)

Question 13

What is 2nd Normal Form?

Answer 13

Must be satisfying 1st Normal Form, and partial key dependencies are removed.

A partial key dependency occurs when a non-key attribute doesn’t depend on the whole of the composite key

Question 14

What is 3rd Normal Form?

Answer 14

Must conform to 2nd Normal form, and the database must have NO non-key dependencies.

“All non-key attributes depend on the key, the whole key, and nothing but the key”

Question 15

What is a Foreign Key?

Answer 15

A linking attribute that joins two tables in a relational database by being a primary key in one and a foreign key in another.

Question 16

What is a Relational Database?

Answer 16

A database where separate tables are made for each entity, and relationships between entities are represented by foreign keys.

Question 17

What is Record Locking?

Answer 17

When a record is accessed by one user, it is immediately locked yo other users until the first has finished using it. Other users are blocked from accessing or modifying the content of a field until it has been unlocked.

Question 18

What is Serialisation?

Answer 18

Rather than locking the field, requests from other users are placed in a queue. Once the first user has finished using the field, the next command in the queue is executed and so on.

Question 19

What is Timestamp Ordering?

Answer 19

When multiple commands are sent to the same field in a database, each is assigned a timestamp which marks the point in time at which the command was initiated. Commands are carried out on the field in the order of their timestamps.

Question 20

What is Commitment Ordering?

Answer 20

An algorithm is used to work out an optimum order in which to execute commands for the same field. This algorithm will take into account the impact of commands on other parts of the database and attempt to minimise issues from occurring with the database.