1.3.2 Databases

Question 1

what is a database

Answer 1

A database is nothing more than an organised collection of data. ​

Organising data into a database allows for easy:​

Adding​

Modification​

Deletion​

Searching​

Question 2

Relational Databases

Answer 2

An entity is an item of interest about which information is stored. A relational database is a recognises the differences between entities by creating different tables for each entity

Question 3

Flat File

Answer 3

A flat file is a database that consists of a single file. The flat file will most likely be based around a single entity and its attributes.

Very simple, quick to set up, require little expertise to maintain and are suitable for storing small amounts of data.

Question 4

Primary Key

Answer 4

A primary key is a unique identifier for each record in the table.

Question 5

Foreign Key

Answer 5

A foreign key is the attribute which links two tables together. The foreign key will exist in one table as the primary key and act as the foreign key in another.

Question 6

Secondary Key

Answer 6

A secondary key allows a database to be searched quickly.

Question 7

Normalisation

Answer 7

Normalisation tries to accomplish the following things:

1. All field names must be unique
2. Values in fields should be from the same domain
3. Values in fields should be atomic
4. No two records can be identical
5. Each table needs a primary key

Question 8

First Normal Form

Answer 8

There must be no attribute that contains more than a single value.

Question 9

Second Normal Form

Answer 9

A database which doesn’t have any partial dependencies and is in first normal form can be said to be in second normal form. This means that no attributes can depend on part of a composite key.

Question 10

Third Normal Form

Answer 10

If the database is in second normal form and contains no non-key dependencies, it is in third normal form. A non-key dependency means the attribute only depends on the value of the primary key and nothing else

Question 11

Indexing

Answer 11

Indexing is a method used to store the position of each record ordered by a certain attribute. This is used to look up and access data quickly. The primary key is automatically indexed

Question 12

Capturing Data

Answer 12

Data needs to be input into the database and there are various ways of doing this. The chosen method is always dependent on the context. For example, if pedestrians are participating in a survey, their responses will need to be manually entered.

Data is also captured when people pay cheques. Banks scan cheques using Magnetic Ink Character Recognition (MICR). Optical Mark Recognition (OMR) is used for multiple choice questions on a test. Other forms use Optical Character Recognition (OCR).

Question 13

Selecting and Managing Data

Answer 13

Selecting the correct data is an important part of data preprocessing. This could involve only selecting data that fits a certain criteria to reduce the volume of input. Collected data can be managed using SQL to sort, restructure and select certain sections.

Question 14

Exchanging Data

Answer 14

Exchanging data is the process of transferring the data that has been collected. One common example of this is EDI (Electronic Data Interchange).

Question 15

SQL

Answer 15

SQL stands for Structured Query Language and is a declarative Synoptic Link language used to manipulate databases. SQL enables the creating, removing and updating of databases.

Question 16

Referential Integrity

Answer 16

Referential integrity is the process of ensuring consistency. This ensures that information is not removed if it is required elsewhere in a linked database

Question 17

Transaction Processing

Answer 17

A transaction is defined as a single operation executed on data.

Question 18

ACID

Answer 18

Atomicity
Consistency
Isolation
Durability

Question 19

Atomicity:

Answer 19

• A transaction must be processed in its entirety or not at all,

Question 20

Consistency:

Answer 20

• A transaction must maintain the referential integrity rules between linked tables,

Question 21

Isolation:

Answer 21

Simultaneous executions of transactions should lead to the same result as if they
were executed one after the other.

Question 22

Durability

Answer 22

Once a transaction has been executed it will remain so regardless of the circumstances surrounding it, such as in the event of a power cut.

Question 23

Record Locking

Answer 23

-The process of preventing simultaneous access to records in a database is called record locking and it is used in order to prevent inconsistencies or a loss of updates.

-While one person is editing a record, this ‘locks’ the record so others cannot access the same record.