2.5 Databases

Question 1

What is meant by Big Data

Answer 1

Refers to data sets so large and complex that it becomes difficult to process using standard database techniques

Question 2

Data mining

Answer 2

The analysis of a large amount of data in a data warehouse

Question 3

Predictive analysis and Example

Answer 3

consist of a variety of statistical techniques including modelling, machine learning, and data mining.

Example: In business, predictive models analyses patterns found in historical and transactional data to identify patterns that may present risks or opportunities.

Question 4

Data normalisation (1NF,2NF,3NF)

Answer 4

Moving from:
· unnormalised data to 1NF involves ensuring there are no repeating attributes, attributes should be atomic
· 1NF -> 2NF involves ensuring there are no partial dependencies
· 2NF -> 3NF all data items depend on nothing but the primary key

Question 5

Primary key and foreign key

Answer 5

PK - uniquely identifies a record in a database

FK - a field in a table which links to a primary key in another table
enables data in different tables to be linked together

Question 6

Indexes definition

Answer 6

An index is a list of key fields to improve access times to records and sort the records

Question 7

Data consistency definition

Answer 7

For data to be consistent, it must be added only if it satisfies the rules of the database.

Question 8

Different views of the data

3 points

Answer 8

allow users to access/read/write to/amend/delete only part of DB

Allow database users to access only certain records or certain fields

May link tables together so users view is as if only one table

Question 9

Describe three problems associated with paper-based systems and how computerised databases could solve these problem

Answer 9

1. Difficult and time consuming to amend/easy to make mistakes
   S. It is easy to amend / update data in a database to minimise errors
2. Difficult to encrypt so accessible if stolen
   S. Easy to encrypt so not compromised if stolen
3. Difficult for multiple persons to look at the same record
   S. Many people can view the same record (only one can update)

Question 10

Describe four benefits (for the college) of using a computerised database system.

Answer 10

· Database would be easy to and quick to search for a student or course details

· Easy to back up student or course details in a computerised database

· It is easy to overwrite / amend / update student or course details in a database

· Database allows different access rights for different college staff

Question 11

Verification and it’s purpose

Answer 11

Verification checks are carried out when data is being entered and when data is being transferred from one place to another

Purpose is to ensure data are consistent and ensure data have not been corrupted

Question 12

Double entry verification

Answer 12

Ask customer to type password twice and compare both inputs to check that they are the same

Question 13

Data validation techniques

Answer 13

…

Question 14

Data dictionary definition

Answer 14

A list of information about all the fields used in a database
It will usually include the table names, fields, primary keys and the field validation

Question 15

Outline the role of a database administrator

Answer 15

The person in a company who is responsible for the structure, security and management of the database system and the data in it

Question 16

Describe why distributed databases are often used and identify one difficulty associated with using distributed databases. Explain what is actually distributed in a distributed database.

Answer 16

It is often more efficient to store data on a number of different computers to maximise performance.

It is difficult to ensure that all the data in all the computers is always up-to-date / maintain integrity.

Both processing and data are distributed across the different computers that the data is stored upon

Question 17

How a random access file operates

6 Marks

Answer 17

· Physical location for new record is calculated from the key field
· A hashing algorithm is used for this calculation to find the location
· If data collision /something there, the record is stored instead in an overflow area
· Data in the overflow area is normally stored and searched in a linear manner
· File may need reorganising if overflow becomes too large
· Existing records are accessed in the same way.

Question 18

Explain what is meant by data normalisation in a relational database. With benefits

Answer 18

Normalisation:
· is a way of structuring data according to theoretical rules
· normalising data usually reduces data duplication/redundancy
· avoids danger of inconsistency / maintains integrity
· avoids danger of data being lost during update
· avoids wasting processing time
· probably enables easier maintenance of the database
· allows different views of the data

Question 19

Describe the difference between flat file and relational database systems

Answer 19

A flat file system may contain a number of single tables with no links between them, whereas a relational database normally contains a number of linked tables

Question 20

Advantages of using a distributed database

5 Marks

Answer 20

· Resilient. A problem in one site will not stop other sites from working.
· Security. Staff access can be limited to only their portion of the database.
· Network traffic is reduced so reducing bandwidth costs.
· A single site database still works even if the connection between sites is temporarily broken
· Expense: either cheaper or more expensive but has to be properly qualified

Question 21

Advantages of a relational over a flat file

Answer 21

Redundancy is reduced

Risk of inconsistent data is reduced

Data independence allows different views of the same data

Allows easy extension to the structure of the database