Relational Data Model

Question 1

3 components of the relational data model

Answer 1

1. a structural part - set of rules
2. amanipulative part - operations allowed on data
3. a set of integrity constraints

Question 2

define relation

Answer 2

table with columns and rows

Question 3

what data type is a row in a relation

Answer 3

tuple

Question 4

define attribute

Answer 4

named column of a relation

Question 5

define domain

Answer 5

a set of allowable values for one or more attributes

Question 6

define degree

Answer 6

number of attributes in a relation

Question 7

example of 3 types of degrees

Answer 7

1. unary - 1
2. binary - 2
3. ternary - 3

Question 8

define cardinality

Answer 8

number of tuples in a relation

Question 9

define relational database

Answer 9

collection of normalised relations with distinct relation names

Question 10

properties of relations

Answer 10

• name is distinct
• each cell contains exactly one single value
• each attribute has a distinct name
• values of an attribute are from the same domain
• each tuple is distinct
• order of attributes has no significance
• order of tuples has no significance

Question 11

define candidate key

Answer 11

a super key such that no proper subset is a super key within a relation

Question 12

what are the 2 properties of a candidate key

Answer 12

1. uniqueness
2. irreducibility

Question 13

what does irreducibility mean in candidate keys

Answer 13

no proper subset of K has the uniqueness property

Question 14

define primary key

Answer 14

the candidate key that is used to uniquely identify a tuple within a relation

Question 15

define foreign key

Answer 15

an attribute, or set of attributes, within one relation that matched the primary (or candidate) key of some relation

Question 16

what are integrity constraints

Answer 16

set of rules to ensure the data is accurate by controlling the types of data that can be entered into a table

Question 17

what are the 2 main integrity constraints

Answer 17

1. entity integrity
2. referential integrity

Question 18

describe entity integrity

Answer 18

• every relation must have a primary key and the primary key must not contain null values
• implemented through primary key constraint

Question 19

describe referential integrity

Answer 19

• if a foreign key exists in a relation:
  ○ 1 - either the foreign key value must match a candidate key value of some tuple in its home relation or
  ○ 2 - the foreign key values must wholly be null
• implemented through the foreign key restraint

Question 20

what is null

Answer 20

represents a value of an attribute that is currently unknown or is not applicable for this tuple

Question 21

why do we use null

Answer 21

way to deal with incomplete or exceptional data

Question 22

define general constraints

Answer 22

additional rules specified by the users or database administrator