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Database > Relationship Model > Flashcards

Relationship Model Flashcards

1
Q

Hierarchical Database

A

1970 IBM Information Management System

1:M relationship

A tree of linked records

child has only one parent (limitation)

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2
Q

Network Database

A

Intergrated Data Store

Child have multiple parents

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3
Q

Navigational Database

A

Move around in data via pointers or links

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4
Q

Relational Model

A

basic structure is the mathematical concept

Relation
Table
Storage

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5
Q

Relation

A

Abstract object

Heading (fixed)
Body (varies over time)

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6
Q

Table

A

Pictorial representation

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7
Q

Domain

A

Set of atomic values which specifies

name, data type and data format

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8
Q

Relation Heading

A

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

each attribute (column) corresponds to an underlying domain

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9
Q

Relation cardinality

A

number of tuples

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10
Q

Relation body

A

aka Relation instance

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11
Q

Relation instance

A

State of the relation at any point in time

Consist of tuples (rows)

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12
Q

Relation degree

A

no of attributes

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13
Q

Tuples in Relation

A 
No duplicate
Unique
Inordered in a relation
Attributes not ordered in a tuple
Atomic (cannot be divided)
Not multivalued
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14
Q

Functional Dependency

A

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

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15
Q

Candidate key

A

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

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16
Q

Primary Key

A

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

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17
Q

Alternate Key

A

Remaining keys that are not the primary key

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18
Q

Composite key

A

A primary key comprising of many attributes

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19
Q

How to Select Primary Key

A

Unique

Nonintelligent

No change over time

Single attribute

Numeric

Security Compliant

20
Q

Null

A

no value

21
Q

Why Null

A

Value not applicable

Value unknown

Value does not exist

Value undefined

22
Q

Relational database

A

A collection of normalised relations

23
Q

Foreign Key

A

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

24
Q

Referential Integrity

A

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

25
Q

Entity integrity

A

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

26
Q

Column/Domain integrity

A

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

27
Q

Relational algebra

A

relational
input = relation
output = relation

procedural

operators only apply to at most two relations at a time

28
Q

8 basic operations of relational algebra

A

single relation (selection, projection)

cartesian product, join

union

intersection

difference

division

29
Q

π

A

pi -> Project

vertical selection
of a relation to create a new relation

only unique tuples are shown in output

30
Q

σ

A

sigma -> Select

horizonal selection of a relation

a new relation is then created

selection via content i.e. define data for the corresponding tuple

31
Q

Union (U)

A

combines all rows from two relation that are union compatible

excludes duplicate rows

32
Q

Intersect (∩)

A

combines rows that appear in two relations

must be union compatible

33
Q

Difference (-)

A

rows in one relation that does not appear in another

BUT

Table A-Table B does not equal to Table B-Table A

34
Q

Product (X)

A

yields all possible rows from two relations

cartesian product

35
Q

Cartesian Product

A

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

36
Q

Tuple

A

A table row in relational model

37
Q

Domain

A

a set of attributes

38
Q

Composite primary key

A

more than one primary key

39
Q

Key

A

one or more attributes that determine other attributes

used to establish relationships among relations

determination

40
Q

Determination

A

The role of a key

An attributes value can be looked up/determined by another attribute value

41
Q

Determinant

A

an attribute whose value determines other values in

42
Q

Dependent

A

an attribute whose value is determined by another attribute

43
Q

Key attribute

A

an attribute that is part of a primary key

44
Q

Composite key

A

a multiple-attribute key

45
Q

Superkey/Key

A

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

46
Q

Full functional dependency

A

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

47
Q

Secondary key

A

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

Database (3 decks)

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