Class 03.

Question 1

what are entities?

Answer 1

the database “nouns” (signal the problem)

Question 2

what are attributes?

Answer 2

characteristics of entities

Question 3

what is a key attribute?

Answer 3

a unique identifier

Question 4

what are multi varied attributes?

Answer 4

more than one values for an attribute (ie. address + number)

Question 5

what is a composite attribute?

Answer 5

an attribute of an attribute

Question 6

what is a candidate key?

Answer 6

the minimal set of attributes we can identify a record with + non-duplicate (one of these are the primary keys)

Question 7

what are relationships?

Answer 7

how entities relate (the verbs)

Question 8

T/F: relationships can’t have attributes

Answer 8

false

Question 9

what is cardinality?

Answer 9

“at most one” participation

Question 10

identify a many-to-one relationship

Answer 10

arrow on one side

Question 11

identify a one-to-one relationship

Answer 11

arrows on both sides

Question 12

what is participation constraint?

Answer 12

“at least one” participation

Question 13

what are subclasses?

Answer 13

child of a parent entity connected by a merge (ie. grad vs undergrad)

Question 14

what is a ERD pitfall to avoid?

Answer 14

over-specifiying attributes

Question 15

how to create an ERD?

Answer 15

1. list entities
2. list attributes
3. confirm primary keys
4. establish relationships
5. confirm cardinalities
6. confirm participation constraints