Class 04.

Question 1

what are relational model terminology?

Answer 1

1. row = tuple/entity
2. column = attribute
3. table = relation

Question 2

what are table requirements?

Answer 2

1. attributes have unique names
2. attribute values are the same
3. each cell contains single value
4. non-duplicate rows

Question 3

what do null values indicate?

Answer 3

missing information

Question 4

what is a schema?

Answer 4

describes the content/relationship/structure of data

Question 5

what does the schema include in a relational model?

Answer 5

1. table name
2. column name
3. data type

Question 6

how to convert an ERD to a model with the same attributes?

Answer 6

1. underline primary keys
2. composite attributes in separate columns
3. multivariate attributes in separate tables

Question 7

what is a relationship set?

Answer 7

1. attributes are the primary keys
2. attributes that apply to the relationship itself

Question 8

how to convert many-to-one relationship sets?

Answer 8

1. eliminate separate relation for the relationship
2. capture the relationship on the “many” side
3. “null” entity values that don’t participate in the relationship

Question 9

how to convert one-to-one relationship sets?

Answer 9

1. choose which side to capture the relationship on

Question 10

how to convert many-to-many relationship sets?

Answer 10

1. separate relations whose attributes are primary keys of participating entity sets
2. and attributes that apply to the relationship itself

Question 11

what is the primary key in many-to-many relationships?

Answer 11

the union of the primary keys of the entity

Question 12

T/F: you separate the relation for many-to-one + one-to-one relationship sets

Answer 12

false

Question 13

what is a foreign key?

Answer 13

an attribute in one relation that takes value from the primary key attributes of another relation

Question 14

what is the best way to represent subclasses as relations?

Answer 14

using a foreign key to the superclass

Question 15

how do you map higher order relationships?

Answer 15

create separate relation with attributes taken from the union of primary keys

Question 16

what if there’s a cardinality constraint in the higher order?

Answer 16

entity on the “one” side should not be part of the primary key