Relational Model

Question 1

What is a relation schema?

Answer 1

Named relation followed by set of attributes e.g. Branch(branchNo, street, city, postcode)

Question 2

Can a single attribute have multiple values in a relational schema?

Answer 2

No

Question 3

How do you identify a primary key in a relational schema?

Answer 3

Listed first, underlined and declared explicitly

Question 4

What is the degree of a relational model?

Answer 4

Number of attribute columns

Question 5

What is the cardinality of a relational model?

Answer 5

Number of rows

Question 6

What is a domain in relational schema?

Answer 6

Set of allowed values for attributes

Question 7

What is null?

Answer 7

An uknown or not applicable value in a row

Question 8

How do you identify a foreign key in a relational schema?

Answer 8

Declared explicitly

Question 9

How is an entity type translated?

Answer 9

Each type becomes its own relational schema with certain special attributes being translated differently

Question 10

How are composite attributes translated?

Answer 10

Broken down into separate attributes in its entities schema

Question 11

How are multi-valued attributes translated?

Answer 11

Becomes its own relational schema with its attribute, foreign key of entity, and composite primary key of them both

Question 12

How are derived attributes translated?

Answer 12

Not necessary to store, and are not included

Question 13

How are weak entity types translated?

Answer 13

Becomes a relational schema with its attributes and a composite key of its dependant relationship’s primary key and its own partial key

Question 14

How are 1:M relationships translated?

Answer 14

Add to attribute list of the child entity (M side) a foreign key of the parent’s (1 side) primary key e.g. Staff(staffNo, lname, branchNo)

Question 15

How are 1:1 relationships translated?

Answer 15

treated as 1:M where the child is chosen as the one with total participation (if possible) e.g. Staff(staffNo, lname, branchNo)

Question 16

How are M:M relationships translated?

Answer 16

New schema created, including relationship attributes, foreign keys as primary keys of each participating entities, where the primary is a composite of all foreign keys e.g. Views(clientNo, propNo, viewDate)

Question 17

How are recursive relationships translated?

Answer 17

Treated like any other relationship, but foreign key must differ to maintain distinct attribute names e.g. Staff(saffNo, lname, supervisor)

Question 18

How are non binary relationships translated?

Answer 18

New relation schema including all foreign keys of participating entities primary keys, picking the relations primary key as all foreign keys of parent entities e.g. Registers(clientNo, _staffNo, branchNo, startDate)