Databases & Big Data

Question 1

What is an entity?

Answer 1

Data inside of a database to be stored.

Question 2

What are attributes?

Answer 2

Characteristics of other information about entities.

Question 3

What is an entity identifier?

Answer 3

Unique attribute given to an entity.

Question 4

What is an entity description?

Answer 4

Describes how information about data is stored in the table.

Question 5

What are Relational Databases?

Answer 5

Idea that tables within a database can be related - linked with common attributes.

Question 6

What is a primary key in databases?

Answer 6

Attribute which provides a unique identifier for every identity within table.

Question 7

What is a foreign key?

Answer 7

Attribute within table which is the primary key of another table.

Question 8

What is a composite primary key?

Answer 8

Primary key formed by a combination of attributes.

Question 9

Why are databases normalised?

Answer 9

Allow efficiency without compromising integrity of data.
Ensures no redundant or repeated data.

Question 10

What is first normal form?

Answer 10

First stage of normalisation

Database table will contain no repeating attributes
Atomic - No column contains more than one value.

Question 11

What is second normal form?

Answer 11

Partial keys dependencies removed
- Attributes not dependant on the whole composite key.

Question 12

What is third normal form?

Answer 12

Database fits second form, and has no non-key dependencies.

Question 13

What are client-server databases?

Answer 13

Database which allows simultaneous access for multiple clients.

Question 14

What is concurrent access?

Answer 14

When 2 users attempt to request access to the same fields at the same time.
Result in database updates being lost.

Question 15

How can concurrent access issues be managed?

Answer 15

Record locks .
Serialisation
Timestamp / commitment ordering.

Question 16

What are record locks?

Answer 16

Record locked when user has accessed it. Unlocked when user finished using it.

Question 17

What is serialisation

Answer 17

Requests from other user placed in a queue - When first user finished, the next command in queue is executed.

Question 18

What is timestamp / commitment ordering?

Answer 18

Timestamp - Commands executed in order of timestamps of sent request.
Commitment - Algorithm used to work out optimum order in which to execute commands - impact of commands etc to minimise issues from occurring.

Question 19

What is Big Data?

Answer 19

Term used for data which won’t fit in usual containers.

Question 20

What are the 3 defining features of Big Data?

Answer 20

Volume - Too much data for conventional HDD or servers - Has to be spread over multiple servers.

Velocity - Data on servers modified and created rapidly.

Variety - Data held on servers consist of many different types of data - Binary, multimedia etc.

Question 21

What is the main problem plaguing Big Data?

Answer 21

Lack of structure - not massively volume of data.

Question 22

How is machine learning being used in Big Data?

Answer 22

Unstructured nature of Big Data makes it hard to extract useful information - Machine learning used to discern patterns in data.

Question 23

What is Functional Programming?

Answer 23

Solution to problem of processing data over multiple machines.

Question 24

How does functional programming work?

Answer 24

Programs are stateless and use immutable data structures.
Supports higher-order function - Using functions as inputs and outputs.

Question 25

What is the fact-based model for representing data?

Answer 25

Big data doesn’t store well in columns and tables.
Using immutable data removes risk of data being lost from human error, removes need for index and new data simply appended as dataset is created.

Question 26

How does the fact-based model work to store data?

Answer 26

Information stored as an immutable fact.
Stored with a timestamp - allow computer to use most recent information.

Question 27

How is Big Data represented using Graph Schema?

Answer 27

Graph Schema - using graphs of nodes and edges to graphically represent structure of dataset - Nodes are entities, edges are relationships.