Data relations(1.3.2 1)

Question 1

What are relational databases?

Answer 1

usually created of 2D data structures called tables

Question 2

What are table identifiers?

Answer 2

each table in the database needs a name

Question 3

What is a record?

Answer 3

each row in a table

Question 4

What is a field?

Answer 4

each column a table

Question 5

What is a data element/data item?

Answer 5

each individual cell in a table

Question 6

Table and field identifier

Answer 6

case sensitive
should contain no spaces

Question 7

Tables and keys

Answer 7

the most important aspect of a table (even in a flat file) is that each record must be unique;y identifiable in some way
to do this we define a primary key

Question 8

What is a primary key?

Answer 8

a field or collection of fields which uniquely identify each record

Question 9

ID fields

Answer 9

an easy way to create a uniquely identifiable record is to simply have a field which contains an automatically generated ( often serialised) ID number
it increase the size of the database
it introduces an abstrxct piece of data which may have no relevence to real life uses

Question 10

What is a foreign key?

Answer 10

a field of one table which references the primary key of a different table

Question 11

Foreign keys

Answer 11

using one produces a relation between the two tables
tables can be related to multiple other tables by use of foreign key
cannot be used as the primary key in a related table and should not be used as part of a multi field primary key

Question 12

Entities and relations

Answer 12

we can describe the relation between the tables by considering the actual relation between the objects described in the table

Question 13

One to many relation

Answer 13

Question 14

One to one relation

Answer 14

Question 15

Many to many relation

Answer 15

Question 16

Linking tables

Answer 16

the inclusion of a linking table splits the many to many relation into two different one to one relations

Question 17

Primary key and indexing

Answer 17

a primary key is automatically indexed within a database
an indexed field is very easily searched and records are quickly retrieved

Question 18

Secondary key and indexing

Answer 18

can define a field as a secondary key which the database will then index
makes searching and retrieving records via secondary key much quicker at the cost of increasing the storage space required by the database

Question 19

Data

Answer 19

raw and unprocessed (can contain error)
needs processing before we can get any information out of it
can come from automated or human sources

Question 20

How to get data automated sources

Answer 20

e.g electronic sensors (weather stations presence detectors web cookies)
produces huge amounts of data cheaply
sensor errors can go unnoticed for a long time
ethical concerns (surveillance anonymity)

Question 21

How to get data human sources

Answer 21

e.g census survey
error prone (due to human error)
expensive
difficult to get people to to voluntarily provide private data

Question 22

Turning data to information

Answer 22

data needs to be cleaned (removing any errors)
statistical methods/graphical methods can be applied to the data
visualisations are great all about making it easier for the person looking at it
correlation vs causation

Question 23

Storing data

Answer 23

easiest way to store data is a table
rows are records
columns are fields

Question 24

Flat file database

Answer 24

single table of data
requires no specialised software
portable (flat files are often stored in plain text)
easy to use (requires no specialist training)
large datasets start to become unwieldy (errors can become more prevalent)