week 1 Relational Models and Relational Algebra

Question 1

Rows in the database represent

Answer 1

entities

Question 2

Columns in the database represent

Answer 2

attributes

Question 3

Are tuples ordered or unordered

Answer 3

unordered

Question 4

cardinality

Answer 4

Cardinality refers to the relationship between a row of one table AND a row of another table. The only two options for cardinality are one OR many.

Example: Think of a credit card company that has two tables: a table for the person who gets the card and a table for the card itself.

Question 5

Does each column have a domain

Answer 5

Yes each column have a domain. That is the value of the domain

Question 6

Relation is also know as what in the course

Answer 6

Table

Question 7

What is a procedural database language

Answer 7

Relational Algebra - Instructs the system to perform a sequence of operations to compute a results

Question 8

What a non- procedural/ Declarative language

Answer 8

SQL / Relational Calculus - Tells what data is to be retrieved but does not tell the system how to retrieve the data

Question 9

Relational Algebra - union

Answer 9

r U s = (what is in both tables) (add both tables)

Question 10

Relational Algebra - difference

Answer 10

r -s = (difference between the two tables)

List IS NOT

Remove all like elements in both tables and the result is what is left over

Question 11

Relational Algebra - cartesion product

Answer 11

r x = (all the rows in both)

Basically both tables combined (one big ass table or results)

Combines Columns

Question 12

Relational Algebra - Selection

Answer 12

select a few rows in the relation on a condition

Sigma works on one operator

Filter everything except what you are looking for

It filters certain tuples in a relation based on given criteria.

Question 13

Relational Algebra - Projection

Answer 13

Returns a set up attributes (only returns the a selected)

Symbol Pi

Just return some fields (columns)

Question 14

Given two tuple sets (A with 10 elements and B with 5 elements), what is the maximum number of tuples in the union of these sets?

1) 5
2) 15
3) 10
4) 60

Answer 14

2) 15

Question 15

Which mathematical operator must be used in order to display information about students who are majoring in Computer Science but not in Electrical Engineering?

1) Difference
2) Intersection
3) Union
4) cartesion product

Answer 15

1) Difference

Question 16

Which statement about the selection operator is true?

1) It filters certain attributes in a relation based on given criteria.
2) It requires more than one relation as its input.
3) It requires more than one database as its input.
4) It filters certain tuples in a relation based on given criteria.

Answer 16

It filters certain tuples in a relation based on given criteria.

Question 17

Relational Algebra - Intersection

Answer 17

Returns what is the same in both tables.

Common tuples

Question 18

Join is similar to what

Answer 18

Similar to cartesion product, BUT it requires a common selection (like a common id)

Question 19

Consider a relation, STUDENT, with the following attributes: Name, ID number, Major, Graduation Year, and GPA. Consider a query using this relation: “List the names and ID numbers of students majoring in Computer Science.” Which operator is absolutely necessary for this query?

1) Union
2) Difference
3) Intersection
4) Projection

Answer 19

4) Projection

Question 20

What is the ϴ-Join operation used for?

1) To join two tuples in the same relation.
2) To join two attributes in the same relation.
3) To join two relations in a database.
4) To join two databases.

Answer 20

To join two relations in a database.

Question 21

Which statement about the selection operator is correct? (checkbox)

1) It displays certain tuples based on given criteria.
2) It displays certain attributes based on given criteria.
3) It requires more than one relation.
4) The selection operator can work on a relation even with a single attribute.

Answer 21

1) It displays certain tuples based on given criteria.

This is the output of the selection operator.

4)The selection operator can work on a relation even with a single attribute.

This makes sense too.