DATABASE MANAGEMENT SYSTEM POLYTECHNICch2.ppt

Database System Concepts, 6th
Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Chapter 2: Intro to Relational Model
Chapter 2: Intro to Relational Model

2.2
Database System Concepts - 6th
Edition
Example of a Relation
Example of a Relation
attributes
(or columns)
tuples
(or rows)

2.3
Edition
Attribute Types
Attribute Types
 The set of allowed values for each attribute is called the domain
of the attribute
 Attribute values are (normally) required to be atomic; that is,
indivisible
 The special value null is a member of every domain
 The null value causes complications in the definition of many
operations

2.4
Edition
Relation Schema and Instance
Relation Schema and Instance
 A1, A2, …, An are attributes
 R = (A1, A2, …, An ) is a relation schema
Example:
instructor = (ID, name, dept_name, salary)
 Formally, given sets D1, D2, …. Dn a relation r is a subset of
D1 x D2 x … x Dn
Thus, a relation is a set of n-tuples (a1, a2, …, an) where each ai  Di
 The current values (relation instance) of a relation are specified by
a table
 An element t of r is a tuple, represented by a row in a table

2.5
Edition
Relations are Unordered
Relations are Unordered
 Order of tuples is irrelevant (tuples may be stored in an arbitrary order)
 Example: instructor relation with unordered tuples

2.6
Edition
Database
Database
 A database consists of multiple relations
 Information about an enterprise is broken up into parts
instructor
student
advisor
 Bad design:
univ (instructor -ID, name, dept_name, salary, student_Id, ..)
results in
 repetition of information (e.g., two students have the same instructor)
 the need for null values (e.g., represent an student with no advisor)
 Normalization theory (Chapter 7) deals with how to design “good”
relational schemas

2.7
Edition
Keys
Keys
 Let K  R
 K is a superkey of R if values for K are sufficient to identify a unique
tuple of each possible relation r(R)
 Example: {ID} and {ID,name} are both superkeys of instructor.
 Superkey K is a candidate key if K is minimal
Example: {ID} is a candidate key for Instructor
 One of the candidate keys is selected to be the primary key.
 which one?
 Foreign key constraint: Value in one relation must appear in another
 Referencing relation
 Referenced relation

2.8
Edition
Schema Diagram for University Database
Schema Diagram for University Database

2.9
Edition
Relational Query Languages
Relational Query Languages
 Procedural vs.non-procedural, or declarative
 “Pure” languages:
 Relational algebra
 Tuple relational calculus
 Domain relational calculus
 Relational operators

2.10
Edition
Selection of tuples
Selection of tuples
 Relation r
 Select tuples with A=B
and D > 5
 σ A=B and D > 5 (r)

2.11
Edition
Selection of Columns (Attributes)
Selection of Columns (Attributes)
 Relation r:
 Select A and C
Projection
Π A, C (r)

2.12
Edition
Joining two relations – Cartesian Product
Joining two relations – Cartesian Product
 Relations r, s:
 r x s:

2.13
Edition
Union of two relations
Union of two relations
 Relations r, s:
 r  s:

2.14
Edition
Set difference of two relations
Set difference of two relations
 Relations r, s:
 r – s:

2.15
Edition
Set Intersection of two relations
Set Intersection of two relations
 Relation r, s:
 r  s

2.16
Edition
Joining two relations – Natural Join
Joining two relations – Natural Join
 Let r and s be relations on schemas R and S respectively.
Then, the “natural join” of relations R and S is a relation on
schema R  S obtained as follows:
 Consider each pair of tuples tr from r and ts from s.
 If tr and ts have the same value on each of the attributes in
R  S, add a tuple t to the result, where
 t has the same value as tr on r
 t has the same value as ts on s

2.17
Edition
Natural Join Example
Natural Join Example
 Relations r, s:
 Natural Join
 r s

2.18
Edition
Figure in-2.1
Figure in-2.1

Database System Concepts, 6th
Ed.
See www.db-book.com for conditions on re-use
End of Chapter 2
End of Chapter 2

2.20
Edition
Figure 2.01
Figure 2.01

2.21
Edition
Figure 2.02
Figure 2.02

2.22
Edition
Figure 2.03
Figure 2.03

2.23
Edition
Figure 2.04
Figure 2.04

2.24
Edition
Figure 2.05
Figure 2.05

2.25
Edition
Figure 2.06
Figure 2.06

2.26
Edition
Figure 2.07
Figure 2.07

2.27
Edition
Figure 2.10
Figure 2.10

2.28
Edition
Figure 2.11
Figure 2.11

2.29
Edition
Figure 2.12
Figure 2.12

2.30
Edition
Figure 2.13
Figure 2.13

DATABASE MANAGEMENT SYSTEM POLYTECHNICch2.ppt

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