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Chapter 2: Intro to Relational Model
Database System Concepts, 6th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Database System Concepts
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Chapter 1: Introduction
Part 1: Relational databases
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Chapter 2: Introduction to the Relational Model
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Chapter 3: Introduction to SQL
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Chapter 4: Intermediate SQL
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Chapter 5: Advanced SQL
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Chapter 6: Formal Relational Query Languages
Part 2: Database Design
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Chapter 7: Database Design: The E-R Approach
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Chapter 8: Relational Database Design
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Chapter 9: Application Design
Part 3: Data storage and querying
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Chapter 10: Storage and File Structure
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Chapter 11: Indexing and Hashing
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Chapter 12: Query Processing
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Chapter 13: Query Optimization
Part 4: Transaction management
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Chapter 14: Transactions
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Chapter 15: Concurrency control
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Chapter 16: Recovery System
Part 5: System Architecture
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Chapter 17: Database System Architectures
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Chapter 18: Parallel Databases
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Chapter 19: Distributed Databases
Database System Concepts - 6th Edition
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Part 6: Data Warehousing, Mining, and IR
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Chapter 20: Data Mining
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Chapter 21: Information Retrieval
Part 7: Specialty Databases
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Chapter 22: Object-Based Databases
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Chapter 23: XML
Part 8: Advanced Topics
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Chapter 24: Advanced Application Development
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Chapter 25: Advanced Data Types
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Chapter 26: Advanced Transaction Processing
Part 9: Case studies
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Chapter 27: PostgreSQL
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Chapter 28: Oracle
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Chapter 29: IBM DB2 Universal Database
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Chapter 30: Microsoft SQL Server
Online Appendices
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Appendix A: Detailed University Schema
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Appendix B: Advanced Relational Database Model
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Appendix C: Other Relational Query Languages
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Appendix D: Network Model
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Appendix E: Hierarchical Model
2.2
©Silberschatz, Korth and Sudarshan
Chapter 2: Intro to Relational Model
 2.1 Structure of Relational Databases
 2.2 Database Schema
 2.3 Keys
 2.4 Schema Diagrams
 2.5 Relational Query Languages
 2.6 Relational Operations
Database System Concepts - 6th Edition
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Example of a Relation
attributes
(or columns)
tuples
(or rows)
Database System Concepts - 6th Edition
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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
Database System Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
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
Database System Concepts - 6th Edition
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Relations are Unordered
 Order of tuples is irrelevant (tuples may be stored in an arbitrary order)
 Example: instructor relation with unordered tuples
Database System Concepts - 6th Edition
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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
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repetition of information (e.g., two students have the same instructor)
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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
Database System Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
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)
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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.
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which one?
 Foreign key constraint: Value in one relation must appear in another
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Referencing relation
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Referenced relation
Database System Concepts - 6th Edition
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Schema Diagram for University Database
Database System Concepts - 6th Edition
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Relational Query Languages
 Procedural vs.non-procedural, or declarative
 “Pure” languages:
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Relational algebra
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Tuple relational calculus
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Domain relational calculus
 Relational operators
Database System Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
Selection of tuples
 Relation r
 Select tuples with A=B
and D > 5
σ
A=B and D > 5
Database System Concepts - 6th Edition
(r)
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Selection of Columns (Attributes)
 Relation r:
 Select A and C
Projection
Π A, C (r)
Database System Concepts - 6th Edition
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Joining two relations – Cartesian Product
 Relations r, s:
 r x s:
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Union of two relations
 Relations r, s:
 r  s:
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Set difference of two relations
 Relations r, s:
 r – s:
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Set Intersection of two relations
 Relation r, s:
 rs
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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:
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Consider each pair of tuples tr from r and ts from s.
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If tr and ts have the same value on each of the attributes
in R  S, add a tuple t to the result, where
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t has the same value as tr on r

t has the same value as ts on s
Database System Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
Natural Join Example
 Relations r, s:
 Natural Join
 r
s
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Figure in-2.1
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End of Chapter 2
Database System Concepts, 6th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Figure 2.01
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Figure 2.02
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Figure 2.03
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Figure 2.04
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Figure 2.05
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Figure 2.06
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Figure 2.07
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Figure 2.10
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Figure 2.11
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Figure 2.12
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Figure 2.13
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