Relational Algebra

Question 1

Relational Calculus

Answer 1

Higher level, declarative language for relational Databases

Question 2

Product of Relational Calculus operation

Answer 2

New Relation

Question 3

Elements of Relational Calculus

Answer 3

Tuples and Domain

Question 4

Relational Algebra

Answer 4

A procedural query language, which takes instances of relations as input and yields instances of relations as output

Question 5

Groups of Relational Algebra

Answer 5

Set theory operations and relational db specific operations

Question 6

Operations in Relational Algebra Set Ops

Answer 6

UNION, INTERSECTION, DIFFERENCE (MINUS), CARTESIAN PRODUCT (CROSS JOIN)

Question 7

Operations in Relational DB Ops

Answer 7

SELECT, PROJECT, JOIN, RENAME

Question 8

Unary Operations

Answer 8

Operations that apply on a single relation (SELECT, PROJECT)

Question 9

Binary Operations

Answer 9

Operate on two relations by combining related tuples (JOIN)

Question 10

Aggregate Functions

Answer 10

Operations that summarize data from Tables or Joins (SUM, COUNT)

Question 11

Selectivity

Answer 11

Fraction of tuples selected by a Selection Condition

Question 12

Selection Condition

Answer 12

Statement of what data for a Select statement to display

Question 13

Symbol for SELECT in Relational Algebra

Answer 13

σ

Sigma

Question 14

Symbol for Relation in Relational Algebra

Answer 14

R

Question 15

Degree in SELECT

Answer 15

# of attributes in a Relation
(Same as the degree of R)

Question 16

Cascade

Answer 16

Sequence of SELECT statements with a Conjuntive (AND, OR)

Question 17

Commutative

Answer 17

σ (σ(R)) = σ(σ(R))

Question 18

PROJECT

Answer 18

Selects columns from a relation. All tuples are DISTINCT

Question 19

Symbol for PROJECT in Relational Algebra

Answer 19

π

Pi

Question 20

Degree in PROJECT

Answer 20

of attributes in a Relation

Question 21

Multiset

Answer 21

Set of tuples with duplicates. AKA “bag”

Question 22

In-Line Expression

Answer 22

Single line of Relational Algebra depicting results that don’t have a given name.

Question 23

RENAME

Answer 23

Renames a relation or attribute name, aka AS

Question 24

Symbol for RENAME in Relational Algebra

Answer 24

ρ or ϱ, with S as relation name or B as attribute name

Rho

Question 25

Union Compatibility

Answer 25

Relations in question for a binary operation must have

• Same degree (# of attributes)
• Same domain

Question 26

Cartesian Product

Answer 26

AKA Cross Join, binary set operation but doesn’t force Union Compatibility

Question 27

Symbol for Cartesian Product in Relational Algebra

Answer 27

X

Question 28

Symbol for JOIN in Relational Algebra

Answer 28

⋈

Question 29

JOIN

Answer 29

combine related tuples from two relations
into single “longer” tuples.
allows us to process relationships
among relations

Question 30

Notation for JOIN statement

Answer 30

DEPT_MGR ← DEPARTMENT ⋈ Mgr_ssn=Ssn EMPLOYEE

Question 31

THETA JOIN

Answer 31

allows for arbitrary comparison relationships (such as ≥)

Question 32

EQUIJOIN

Answer 32

a theta join using the equality operator (instead of comparison)

Question 33

NATURAL JOIN

Answer 33

an equijoin on attributes that have the same name in each relationship.

Question 34

Complete Set

Answer 34

the set of relational algebra operations {σ,π,∪,ρ,–,×}

any of the other original relational algebra operations can be
expressed as a
sequence of operations from this set

For example, the INTERSECTION operation can be expressed by using UNION and MINUS as follows:
R∩S≡(R∪S) – ((R–S)∪(S–R))

Question 35

Symbol for DIVISION in Relational Algebra

Answer 35

÷

Question 36

DIVISION

Answer 36

Find the values that do not belong in the answer , and remove them from the list of possible answers.

Question 37

Query Tree

Answer 37

data structure that corresponds to a relational algebra expression

input relations of the query as
leaf nodes

relational algebra operations as internal nodes

Question 38

Set of Aggregate Functions

Answer 38

COUNT, SUM, AVERAGE, MAXIMUM, and MINIMUM

Question 39

Symbol for Aggregate Function in Relational Algebra

Answer 39

ℑ

script F

Question 40

Recursive Closure

Answer 40

applied to a recursive relationship between tuples of the same type

example of a recursive operation is to retrieve all supervisees of an employee (e) at all levels—that is, all employees (e’) directly supervised by e all employees
e’’ ℑ directly supervised by each employee e’, all employees e’’’ directly supervised by each employee e’’, etc
,

Question 41

OUTTER JOIN

Answer 41

Join that maintains all the tuples of one or both relations

Question 42

Range Relation

Answer 42

The relation a tuple “ranges over” (or belongs to)

Question 43

Relational Calc Tuple Variable

Answer 43

A variable ranging over a relation that may take any value which is a tuple from that relation

{t|COND(t)}

Question 44

Parts of a Relational Calc Tuple

Answer 44

{t.Fname,t.Lname | EMPLOYEE(t) AND t.Salary>50000}

range relation - EMPLOYEE(t)
selected combination - t.Salary > 50000
requested attribute - t.Fname, t.Lname