Relationship Model

Question 1

Hierarchical Database

Answer 1

1970 IBM Information Management System

1:M relationship

A tree of linked records

child has only one parent (limitation)

Question 2

Network Database

Answer 2

Intergrated Data Store

Child have multiple parents

Question 3

Navigational Database

Answer 3

Move around in data via pointers or links

Question 4

Relational Model

Answer 4

basic structure is the mathematical concept

Relation
Table
Storage

Question 5

Relation

Answer 5

Abstract object

Heading (fixed)
Body (varies over time)

Question 6

Table

Answer 6

Pictorial representation

Question 7

Domain

Answer 7

Set of atomic values which specifies

name, data type and data format

Question 8

Relation Heading

Answer 8

aka Relation schema
consist of a fixed set of attributes (R)

each attribute (column) corresponds to an underlying domain

Question 9

Relation cardinality

Answer 9

number of tuples

Question 10

Relation body

Answer 10

aka Relation instance

Question 11

Relation instance

Answer 11

State of the relation at any point in time

Consist of tuples (rows)

Question 12

Relation degree

Answer 12

no of attributes

Question 13

Tuples in Relation

Answer 13

No duplicate
Unique
Inordered in a relation
Attributes not ordered in a tuple
Atomic (cannot be divided)
Not multivalued

Question 14

Functional Dependency

Answer 14

A set of attributes ‘A’ functionally determines an attribute ‘B’ if, and only if,
for each A value, there is exactly one value of B in the relation. It is
denoted as A → B

A determines B
B depends on A

Question 15

Candidate key

Answer 15

Attribute or set of attributes which exhibits uniqueness at minimum (minimal superkey) - proper subset is not a superkey

Question 16

Primary Key

Answer 16

One or more candidate key that is chosen to be a primary key (primary key or composite primary key)

Question 17

Alternate Key

Answer 17

Remaining keys that are not the primary key

Question 18

Composite key

Answer 18

A primary key comprising of many attributes

Question 19

How to Select Primary Key

Answer 19

Unique

Nonintelligent

No change over time

Single attribute

Numeric

Security Compliant

Question 20

Null

Answer 20

no value

Question 21

Why Null

Answer 21

Value not applicable

Value unknown

Value does not exist

Value undefined

Question 22

Relational database

Answer 22

A collection of normalised relations

Question 23

Foreign Key

Answer 23

An attribute or set of attributes in a relation that exists in the same or another relation as a Primary Key

Question 24

Referential Integrity

Answer 24

A foreign key value must either match the full primary key in a relation or be null

Question 25

Entity integrity

Answer 25

a condition where each row (entity instance) in the relation has its own unique identity The primary key must be unique and not be null

Question 26

Column/Domain integrity

Answer 26

All values in a given column must come from the same domain

Question 27

Relational algebra

Answer 27

relational input = relation output = relation procedural operators only apply to at most two relations at a time

Question 28

8 basic operations of relational algebra

Answer 28

single relation (selection, projection) cartesian product, join union intersection difference division

Question 29

π

Answer 29

pi -> Project vertical selection of a relation to create a new relation only unique tuples are shown in output

Question 30

σ

Answer 30

sigma -> Select horizonal selection of a relation a new relation is then created selection via content i.e. define data for the corresponding tuple

Question 31

Union (U)

Answer 31

combines all rows from two relation that are union compatible excludes duplicate rows

Question 32

Intersect (∩)

Answer 32

combines rows that appear in two relations must be union compatible

Question 33

Difference (-)

Answer 33

rows in one relation that does not appear in another BUT Table A-Table B does not equal to Table B-Table A

Question 34

Product (X)

Answer 34

yields all possible rows from two relations | cartesian product

Question 35

Cartesian Product

Answer 35

No of rows in relation 1 multiply no of rows in relation 2 every tuple in one relation is paired with every tuple in another relation

Question 36

Tuple

Answer 36

A table row in relational model

Question 37

Domain

Answer 37

a set of attributes

Question 38

Composite primary key

Answer 38

more than one primary key

Question 39

Key

Answer 39

one or more attributes that determine other attributes used to establish relationships among relations determination

Question 40

Determination

Answer 40

The role of a key An attributes value can be looked up/determined by another attribute value

Question 41

Determinant

Answer 41

an attribute whose value determines other values in

Question 42

Dependent

Answer 42

an attribute whose value is determined by another attribute

Question 43

Key attribute

Answer 43

an attribute that is part of a primary key

Question 44

Composite key

Answer 44

a multiple-attribute key

Question 45

Superkey/Key

Answer 45

an attribute or set of attributes that can uniquely identify any row in a table

Question 46

Full functional dependency

Answer 46

when an attribute is functionally dependent on an attribute and not any of its proper subset (the determinant is a composite)

Question 47

Secondary key

Answer 47

for data retrieval i.e. customer wont remember their customer ID but a combination of name and telephone will retrieve customer ID no.