3.2.1 Databases 1

Question 1

what is a database

Answer 1

organised collection of data

Question 2

databases consist of…

Answer 2

entities-tables

relationships between entities- created using key fields

Question 3

two types of database

Answer 3

flat file

relational

Question 4

flat file databases

Answer 4

only consist of one file/ table
run onto problems when try to store data about related items eg contacts phone numbers addresses

does not have integrity- cannot reply on information

Question 5

relational databases

Answer 5

store data about separate entities (contacts and companies) in different tables.

more than one table joined by relationships using primary and foreign keys

Question 6

advantages of a relational database

Answer 6

data redundancy reduced- data duplication- cut down on data items.

data inconsistency reduced- inconsistency by product of redundancy.

data integrity- inconsistency reduced- more integrity- integrity result of validation.

access rights-relational db systems allow for different users to be given different rights to data operations. SELECT INSERT DELETE ALTER CREATE

Question 7

an entity

Answer 7

object about which data is stored. each instance of an entity is a record- information about one specific employee or product etc.

Question 8

attributes

Answer 8

describe each individual data item within the entity

Question 9

primary key

Answer 9

uniquely identifies each instance of an entity

Question 10

composite key

Answer 10

uniquely identifies a record using two or more attributes which may be primary keys in other entities.

Question 11

foreign key

Answer 11

a non key field in one table which is the key field in another table. used to create the relationship between the entities.

Question 12

relationship

Answer 12

a link between two entities. cardinality details the number of occurrences that can be involved in a relationship.
1:1 1 record in 1 table relates to only 1 in another- teachers to rooms in a primary school.
1:M 1 order contains many items.
M:N many pupils study many subjects. - Broken down to 1:M in dbases.

Question 13

referential integrity

Answer 13

ensures that the data in one table does not contradict the data in another table.
every foreign key value which exists in a table must have a matching primary key value in a related table.
used to manage the relationships between primary and foreign keys.

LOOK AT NOTES FOR INSTRUCTION.