relational db model

Question 1

types of DB models

Answer 1

hierarchical, network, relational

Question 2

hierarchical DB model

Answer 2

tree-based approach based on parent-child relationships. each record is linked to all its child records (customer -> orders -> items)

Question 3

network DB model

Answer 3

improves hierarchical, allows records to have more than one parent, can access data from multiple points

Question 4

table

Answer 4

“relation”
matrix of intersecting rows and columns

Question 5

entity

Answer 5

object/concept about which data is collected and stored

Question 6

entity instance

Answer 6

row in relational table

Question 7

attributes

Answer 7

characteristics of entity (columns)

Question 8

relationships

Answer 8

connections amongst data, used to connect tables

Question 9

structured query language used for

Answer 9

“what” without “how”

Question 10

t/f: questions do not need to be known at design time

Answer 10

true

Question 11

database

Answer 11

set of relations

Question 12

relation

Answer 12

set of tuples (table)

Question 13

tuple

Answer 13

row of a relation, each cell consists of specific values for particular variable/attribute

Question 14

primary key

Answer 14

cell value that uniquely identifies a tuple

Question 15

foreign key

Answer 15

cell value which is exactly equal to the primary key value in some other relation

Question 16

properties of relations

Answer 16

• every relation must have a distinct name
• each cell of relation is atomic
• each attribute must have distinct name
• values of any attribute must be from same domain
• no duplicate tuples
• particular tuple can have only one value for an attribute
• two different tuples can have same value for an attribute
• order of tuples has no significance
• order of attributes has no significance