Download Chs. 1 + 2

Chapter 1: Introduction
Chapter 2: Intro. To the Relational Model
Database System Concepts, 6th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Database Management System (DBMS)
DBMS is
• Collection of interrelated data, a.k.a. database
(DB for short)
• Set of programs to access the data:
•
Find individual data items or sets
•
•
Modify
•
•
Data mining: Find patterns! (Ch.20)
“Cleaning” … examples
Insert + Delete
Database System Concepts - 6th Edition
1.2
©Silberschatz, Korth and Sudarshan
1.1 Examples of DB Applications
• Banking: transactions
• Airlines: reservations, schedules
• Universities: registration, grades
• Sales: customers, products, purchases
• Online retailers: order tracking, customized
recommendations
• Manufacturing: production, inventory, orders, supply
chain
• Human resources: employee records, salaries, tax
deductions
Database System Concepts - 6th Edition
1.3
©Silberschatz, Korth and Sudarshan
Today’s databases can be very large
There are dozens of companies today with DBs
in the 100 PB (petabyte) range.
The LHC at CERN produces about 25 PB of
data every year, for an estimated 300 PB total
so far.
Hurray for the Higgs boson!
Facebook had about 300 PB in 2014, and its
users are producing about 84 PB a year.
Database System Concepts - 6th Edition
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Robotic data tape storage library at one of the CERN-LHC Tier 1 centers
Source:
http://www.quantumdiaries.org/2012/09/18/higgs-hunting-software/
Database System
Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
Database System
Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
Source:
http://www.digitaltrends.com/computing/amazon-snowmobile-data-migration-cloud-storage-truck/
The University DB example used in our text
Stores info about:
• Instructors
• Students
• Departments
• Course offerings
Application program examples:
• Add new students, instructors, and courses
• Register students for courses, generate class rosters
• Assign grades to students, compute GPAs
• Generate transcripts
Database System Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
Before DBMSs existed, DB applications were
built directly on top of file systems
 The system stores permanent records in various files

If a new dept. is created, then a new file is needed,
to store info about all the instructors in that dept.
 Application programs extract records from, and add
records to, the appropriate files.

Application programs are also needed to enforce the
various rules (constraints), e.g. a student cannot take
more than 6 courses at the same time.
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Drawbacks of using file systems
• Data redundancy and inconsistency

Multiple file formats, duplication of information in different files
• Difficulty in accessing data

Need to write a new program to carry out each new task
• Data isolation — multiple files and formats
• Integrity problems

Integrity constraints (e.g., account balance > 0) become “buried” in
program code rather than being stated explicitly

Hard to add new constraints or change existing ones
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Drawbacks of using file systems (cont.)
• Atomicity of updates
•
Failures may leave database in an inconsistent state with partial
updates carried out
•
Example: Transfer of funds from one account to another should
either complete or not happen at all
• Concurrent access by multiple users
•
Concurrent access needed for performance
•
Uncontrolled concurrent accesses can lead to inconsistencies
 Example:
Two people reading a balance (say $100) and
updating it by withdrawing money (say $50 each) “at the same
time”.
• Security problems
•
Hard to provide user access to some, but not all, data
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Drawbacks of using file systems Conclusion
•
Redundancy
•
Inconsistency
•
Difficulty of access
•
Isolation
•
Integrity
•
Atomicity
•
Concurrency
•
Security
Try to
remember
3 of these!
DBMSs offer solutions to all the above problems!
Database System Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
Not in text
2.0 Mathematical Concept of Relation
Example relations between the same two sets of objects
Source:System
http://www.math-only-math.com/worksheet-on-functions-or-mapping.html
Database
Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
Not in text
Mathematical Concept of Relation
Extreme cases:
The empty relation and the total relation
a
d
a
d
b
e
b
e
c
f
c
f
Source:System
http://www.math-only-math.com/worksheet-on-functions-or-mapping.html
Database
Concepts - 6th Edition
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Not in text
Mathematical Concept of Relation
Food for thought: How many different relations
exist between these two sets of elements?
a
d
b
e
c
f
Source:System
http://www.math-only-math.com/worksheet-on-functions-or-mapping.html
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Concepts - 6th Edition
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Not in text
Mathematical Concept of Relation
In a Relational DB, the relation is represented by a table
Source:System
http://www.math-only-math.com/worksheet-on-functions-or-mapping.html
Database
Concepts - 6th Edition
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QUIZ: Draw the tables corresponding to the
relations b, c, and d
Source:System
http://www.math-only-math.com/worksheet-on-functions-or-mapping.html
Database
Concepts - 6th Edition
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2.1 Relations and Tables
attributes
(or columns)
tuples
(or rows)
These are
called
4-tuples
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QUIZ
The IDs have 5 digits, the names are strings of 20 characters, the dept.
names are chosen from a set of 50, and the salaries are integers with 6 digits.
How many different tuples can there be?
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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.
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2.2 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 the
Cartesian product
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
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Relations are Unordered!
The order of tuples is irrelevant (so tuples may be stored in
arbitrary order!)
Example: instructor relation with unordered tuples
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We have covered the following textbook
sections: 1.1, 1.2, 2.1, 2.2
See you at 2:40 in the lab!
SCIENCE 206
EOL 1
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©Silberschatz, Korth and Sudarshan
QUIZ
 What is the difference between a Database (DB) and
a Database Management System (DBMS)?
 How was data stored and managed before the
introduction of DB technology?
 Briefly outline three problems with the method above.
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QUIZ
 What is the difference between a relation and a table?
 Explain the following DB concepts:

Domain

Atomic

Null
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QUIZ
Are these different relations/tables?
No, b/c relations are by definition unordered!
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1.3 View of Data
We use abstraction to manage any complex system.
Catalog, tables,
functions, …
Files, hard-disk
blocks …
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Who uses these levels?
DB user
(e.g. Registrar’s
office clerk)
DB programmer
(e.g. the person who
loads data into the DB)
DB Admin
straddles the
levels
DBMS developer
(e.g. Oracle, Teradata)
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Instances and Schemas
 Schema – the logical structure of the database

Example: The database consists of information about a
set of customers and accounts and the relationship
between them

Analogous to the type of a variable in programming (e.g.
array of characters)

Physical schema: database design at the physical level

Logical schema: database design at the logical level
 Instance – the actual content of the database at a
particular point in time

Analogous to the value of a variable (e.g. “Hello, world!”)
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Physical Data Independence = the ability
to modify the physical schema without
changing the logical schema
• This is an example of modularity!
• Applications depend on the logical schema
• In general, the interfaces between the various levels
and components should be well defined so that
changes in some parts do not seriously influence
others.
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Data model = collection of conceptual tools for describing
•
•
•
Data
Data relationships
Data semantics (e.g. constraints)
• Relational
• Entity-Relationship (E-R) model (mainly for DB design)
• Object-based: encapsulation, methods, inheritance (Object-
oriented and Object-relational)
• Semistructured: a “type” does not necessarily mean the
same set of attributes! (XML)
• Other older models:
•
•
Network
Hierarchical
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1.4 and 1.5 DB Languages
Data Manipulation Language (DML)
• For accessing and manipulating the data
• A.k.a. query language
• Two classes of languages
•
Procedural – user specifies what data is required and
how to get those data
•
Declarative (nonprocedural!) – user specifies what is
required without specifying how to do it
• SQL is the most widely used query language … and
declarative.
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SQL example: Find the name of the
instructor with ID 22222
select
from
where
Database System Concepts - 6th Edition
name
instructor
instructor.ID = ‘22222’
1.32
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SQL example: Find the ID and building of instructors in the
Physics dept.
select instructor.ID, department.building
from instructor, department
where instructor.dept_name = department.dept_name
and
department.dept_name = ‘Physics’
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SQL
Queries in a nutshell:
select …
from …
Database System Concepts - 6th Edition
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where…
©Silberschatz, Korth and Sudarshan
QUIZ: SQL
Write a query to find the building where the instructor with ID
10101 works
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QUIZ: SQL
Write a query to find the building where the instructor with ID
10101 works
select department.building
from
instructor, department
where
instructor.dept_name = department.dept_name
and
instructor.ID = 10101
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QUIZ: SQL
Find the name of all instructors in the Comp. Sci. dept.
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QUIZ: SQL
Find the name of all instructors in the Comp. Sci. dept. who
make more than $80,000
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QUIZ: SQL
Find the name of instructors who work in a dept. with a
budget over $ 100,000
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SQL
Application programs generally access databases
through one of
 Language
extensions to allow embedded SQL
 Application
program interface (e.g.,
ODBC/JDBC) which allow SQL queries to be
sent to a database
(Chapters 3, 4 and 5)
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Data Definition Language (DDL)
 Specification notation for defining the database schema
Example:
create table instructor (
ID
char(5),
name
varchar(20),
dept_name varchar(20),
salary
numeric(8,2))
 DDL compiler generates a set of table templates stored in a
data
dictionary
 Data dictionary contains metadata (i.e., data about data)

Database schema

Integrity constraints

Primary key (ID uniquely identifies instructors)

Referential integrity (references constraint in SQL)
– e.g. dept_name value in any instructor tuple must appear in
department relation

Authorization
Database System Concepts -
6th
Edition
EoL
1.41
©Silberschatz, Korth and Sudarshan
QUIZ: SQL
Write SQL DDL code to create a table named account, with
two columns:
 Account number, which is a string of 10 characters
 Balance, which is an integer
Database System Concepts - 6th Edition
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QUIZ: SQL
Write SQL DDL code to create a table named account, with
two columns:
 Account number, which is a string of 10 characters
 Balance, which is an integer
create table account
(account_number char(10),
balance integer)
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1.6.4 Database design
•
Database = multiple relations
•
Information about an enterprise is broken up into parts (relations)
instructor, department, student, advisor, etc.
•
Bad design: place all information in one huge table, e.g.
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Database design
• Bad design: all information in one huge table 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)
•
problems when updating the table
• Normalization theory (Chapter 7) deals with how to design
“good” relations.
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Lets’ break the big table, then!
Do you see a problem with this DB?
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The correct
solution
preserves the
connections in
the data!
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2.3 Keys
Remember:
• Relations are sets of tuples (tables are sets of
rows).
• Mathematical sets cannot, by definition, have
duplicates.
• Therefore, no two tuples in a relation can have
exactly the same attributes.
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QUIZ Keys
Is this a valid table?
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2.3 Keys
No two tuples in a relation can have exactly the
same attributes.
If we look at all columns of the table, the
combinations of values in them are unique, but …
Question: Can we find a smaller set of attributes
whose combination is unique for the given
relation/table?
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QUIZ Keys
What is the smallest key for this table?
Database System Concepts - 6th Edition
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QUIZ Keys
What is the smallest key for this table?
Database System Concepts - 6th Edition
A
B
C
A1
A2
A2
A3
A4
A5
B1
B1
B1
B2
B2
B3
C1
C2
C3
C2
C1
C4
1.52
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Mathematical Notations for Keys
 K is a subset of the attributes of R:
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? Depends on application.
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Schema diagram for University DB:
Look at the keys in each table!
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Individual work (try to solve before the
next class)
End-of-chapter exercises
•
1.1, 1.4, 1.8, 1.9
•
2.1, 2.3, 2.4
Database System Concepts - 6th Edition
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We have covered the following textbook
sections: 1.3, 1.4, 1.5, 1.6.4, 2.3
See you at 2:40 in the lab!
SCIENCE 206
EOL 2
Database System Concepts - 6th Edition
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©Silberschatz, Korth and Sudarshan
QUIZ
What are the data models we mentioned?
• Relational
• Entity-Relationship (E-R)
• Object-based: Object-oriented and Object-relational
• Semistructured: a “type” does not necessarily mean the
same set of attributes! (e.g. XML, JSON)
• Older models:
• Network
• Hierarchical
Database System Concepts - 6th Edition
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QUIZ
 What are the two extreme cases of structuring of
a DB into tables/relations?
 Why is either one bad?
 Name two major players in the DBMS market.
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QUIZ: SQL
• Is SQL a procedural language? Explain.
• Is SQL a DML or a DDL? Explain.
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QUIZ SQL
Write (Postgre)SQL commands to do the following:
 Create a new database electronics
 Create a table circuits in electronics, with two
columns:

Name of chip (e.g. 74LS04)

Type of gates (e.g. NOT)

Nr. of gates on a chip (e.g. 6)
 Delete the whole table
 Delete the whole database
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CREATE DATABASE electronics;
\connect electronics
Must connect to DB to
create table!
CREATE TABLE circuits (
name
varchar(15),
type
varchar(10),
nr_gates integer
);
DROP TABLE circuits;
\connect postgres
DROP DATABASE electronics;
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Cannot drop the DB we
are connected to!
©Silberschatz, Korth and Sudarshan
QUIZ: Keys
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QUIZ: Keys
Practice Exercise 2.1
Consider the following relational DB:
Employee(person_name, street, city)
Works(person_name, company_name, salary)
Company(company_name, city)
What are the appropriate primary keys?
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1.6.1 The DB design process
1. A high-level data model (e.g. the E-R model, see below)
is chosen as a conceptual framework to specify the
requirements
•
DB designer interacts with users (a.k.a. domain experts)
•
Outcome is a (complete) specification of user requirements
2. A data model (e.g. the relational model) is chosen
3. Conceptual design: DB designer translates user
requirements into conceptual schema for the model
chosen
•
What attributes to represent in the DB
•
How to group attributes into tables
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In the language of
section 1.3.2,
conceptual schema
comes before logical
schema!
©Silberschatz, Korth and Sudarshan
1.6.1 The DB design process
3. Conceptual design: DB designer translates user
requirements into conceptual schema for the model
chosen
•
Functional requirements = what kind of operations must
be performed on the data
4. Logical design
•
The result is the logical schema of the DB (e.g. SQL DDL)
5. Physical design
•
The result is the physical schema of the DB (e.g. files, disk
arrays, SAN)
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1.6.2 Example: DB design for the
University DB
Read and understand!
See also Appendix A!
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1.6.3 The E-R model
Detailed coverage to follow in Ch.7.
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SKIP Sections
1.7 through 1.12
READ and TAKE NOTES:
1.13 History of DB Systems
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2.3 (contd.) Using Keys to Connect
Different Relations/Tables
Foreign key constraint: Value in one table must appear in
another

Referencing table (source)

Referenced table (destination)
Example: instructor.dept_name is
a foreign key in instructor.
It references department.dept_name
Important: foreign keys are not keys! (not unique)
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QUIZ: Foreign Keys
Practice Exercise 2.2
Give an example of tuple
insert and an example of
tuple delete that would
cause violations of the
FK constraint.
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2.4 Schema diagrams
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2.4 Schema diagrams
An almost equivalent schema is this (What is missing?)
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2.5 Relational Query Languages
Very little new info. beyond Ch.1 – Read!
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2.5 Relational Operations
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Relational Algebra:
Selection of tuples (rows)
Relation r
Select tuples with A=B and D > 5
σ A=B and D > 5 (r)
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Relational Algebra:
Selection of Columns (Attributes)
Relation r :
Select A and C
A.k.a. projection
Π A, C (r)
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QUIZ: Relational Algebra
Write a relational algebra
expression that returns
those values of A that are
associated with values of C
in between 5 and 15
(inclusive).
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Relational Algebra and SQL
The selection operator σ is analogous to
the SQL clause …
The projection operator P is analogous to
the SQL clause …
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More Relational Algebra
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Joining two relations
Cartesian Product is the most general join
 Relations r, s:
 r x s:
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Joining two relations
Natural join is the most restrictive join
Only attributes with the same name and type are matched!
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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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Practice Exercise 2.6
Explain in words what these
expressions do:
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QUIZ: Relational Algebra
Explain in words what this relational algebra expression returns:
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Individual work (try to solve before the
next class)
End-of-chapter Practice Exercises
2.3, 2.4, 2.5
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Homework for Chs. 1 + 2
--1.11, 1.12, 1.15
--2.8, 2.9, 2.13, 2.14, 2.15
Due next Tuesday, Jan.31
Hint: For the Bank database used in several
exercises, you may use the schema provided
on the next slide.
Database System Concepts - 6th Edition
1.88
©Silberschatz, Korth and Sudarshan
Schema for Bank database (fig.2.15)
Database System Concepts - 6th Edition
1.89
©Silberschatz, Korth and Sudarshan
Text sections covered:
1.1 through 1.6 + 1.13 (History)
Entire Ch.2
EOL 3
Database System Concepts - 6th Edition
1.90
©Silberschatz, Korth and Sudarshan