Slides 1 Introduction

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Introduction to Information Systems

SSC, Semester 6

Lecture 01

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Staff• Instructors:

– Karl Aberer, BC 108, karl aberer at epfl ch– Philippe Cudré-Mauroux, BC 114, philippe cudre-mauroux

at epfl ch– Office hours: by appointment

• TAs:– Gleb Skobeltsyn (exercises)– Martin Rubli (project)

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Communications• Web page: lsirww.epfl.ch

– Lectures will be available here– Homeworks and solutions will be posted here– The project description and resources will be here

• Newsgroup:

– epfl.ic.cours.IIS

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Textbook

Main textbook:

• Databases and Transaction Processing, An application-oriented approachPhilip M. Lewis, Arthur Bernstein, Michael Kifer, Addison-Wesley 2002.

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Other Texts

Many classic textbooks (each of them will do it)• Database Systems: The Complete Book, Hector Garcia-Molina,

Jeffrey Ullman, Jennifer Widom• Database Management Systems, Ramakrishnan• Fundamentals of Database Systems, Elmasri, Navathe• Database Systems, Date (7. edition)• Modern Database Management, Hoffer, (4. edition)• Database Systems Concepts, Silverschatz, (4. edition)

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Material on the Web

SQL Intro

• SQL for Web Nerds, by Philip Greenspun, http://philip.greenspun.com/sql/

Java Technology

• java.sun.com

WWW Technology

• www.w3c.org

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The Course

• Goal: Teaching RDBMS (standard) with a strong emphasis on the Web

• Fortunately others already did it– Alon Halevy, Dan Suciu, Univ. of Washington– http://www.cs.washington.edu/education/course

s/cse444/

– http://www.acm.org/sigmod/record/issues/0309/4.AlonLevy.pdf

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Acknowledgement

• Build on UoW course– many slides– many exercise– ideas for the project

• Main difference– less theory– will use real Web data in the project

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Outline for Today’s Lecture

• Overview of database systems

• Course Outline

• First Steps in SQL

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What is behind this Web Site?

• http://immo.search.ch/

• Search on a large database

• Specify search conditions

• Many users

• Updates

• Access through a web interface

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Database Management Systems

Database Management System = DBMS

• A collection of files that store the data

• A big C program written by someone else that accesses and updates those files for you

Relational DBMS = RDBMS

• Data files are structured as relations (tables)

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Where are RDBMS used ?

• Backend for traditional “database” applications– EPFL administration

• Backend for large Websites– Immosearch

• Backend for Web services– Amazon

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Example of a Traditional Database Application

Suppose we are building a system

to store the information about:

• students

• courses

• professors

• who takes what, who teaches what

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Can we do it without a DBMS ?

Sure we can! Start by storing the data in files:

students.txt courses.txt professors.txt

Now write C or Java programs to implement specific tasks

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Doing it without a DBMS...

• Enroll “Mary Johnson” in “CSE444”:

Read ‘students.txt’Read ‘courses.txt’Find&update the record “Mary Johnson”Find&update the record “CSE444”Write “students.txt”Write “courses.txt”

Read ‘students.txt’Read ‘courses.txt’Find&update the record “Mary Johnson”Find&update the record “CSE444”Write “students.txt”Write “courses.txt”

Write a C/Java program to do the following:

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Problems without an DBMS...

• System crashes:

– What is the problem ?

• Large data sets (say 50GB)– Why is this a problem ?

• Simultaneous access by many users– Lock students.txt – what is the problem ?

Read ‘students.txt’Read ‘courses.txt’Find&update the record “Mary Johnson”Find&update the record “CSE444”Write “students.txt”Write “courses.txt”

Read ‘students.txt’Read ‘courses.txt’Find&update the record “Mary Johnson”Find&update the record “CSE444”Write “students.txt”Write “courses.txt”

CRASH !

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Enters a DBMS

Data files

Database server(someone else’s

C program) Applications

connection

(ODBC, JDBC)

“Two tier system” or “client-server”

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Functionality of a DBMS

The programmer sees SQL, which has two components:• Data Definition Language - DDL• Data Manipulation Language - DML

– query language

Behind the scenes the DBMS has:• Query engine• Query optimizer• Storage management• Transaction Management (concurrency, recovery)

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How the Programmer Sees the DBMS

• Start with DDL to create tables:

• Continue with DML to populate tables:

CREATE TABLE Students (Name CHAR(30)SSN CHAR(9) PRIMARY KEY NOT NULL,Category CHAR(20)

) . . .

CREATE TABLE Students (Name CHAR(30)SSN CHAR(9) PRIMARY KEY NOT NULL,Category CHAR(20)

) . . .

INSERT INTO StudentsVALUES(‘Charles’, ‘123456789’, ‘undergraduate’). . . .

INSERT INTO StudentsVALUES(‘Charles’, ‘123456789’, ‘undergraduate’). . . .

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How the Programmer Sees the DBMS

• Tables:

• Still implemented as files, but behind the scenes can be quite complex

SSN Name Category 123-45-6789 Charles undergrad 234-56-7890 Dan grad … …

SSN CID 123-45-6789 CSE444 123-45-6789 CSE444 234-56-7890 CSE142 …

Students: Takes:

CID Name Quarter CSE444 Databases fall CSE541 Operating systems winter

Courses:

“data independence” = separate logical view from physical implementation

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Transactions

• Enroll “Mary Johnson” in “CSE444”:BEGIN TRANSACTION;

INSERT INTO Takes SELECT Students.SSN, Courses.CID FROM Students, Courses WHERE Students.name = ‘Mary Johnson’ and Courses.name = ‘CSE444’

-- More updates here....

IF everything-went-OK THEN COMMIT;ELSE ROLLBACK

BEGIN TRANSACTION;

INSERT INTO Takes SELECT Students.SSN, Courses.CID FROM Students, Courses WHERE Students.name = ‘Mary Johnson’ and Courses.name = ‘CSE444’

-- More updates here....

IF everything-went-OK THEN COMMIT;ELSE ROLLBACK

If system crashes, the transaction is still either committed or aborted

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Transactions

• A transaction = sequence of statements that either all succeed, or all fail

• Transactions have the ACID properties:A = atomicity (a transaction should be done or undone completely )

C = consistency (a transaction should transform a system from one

consistent state to another consistent state)

I = isolation (each transaction should happen independently of other transactions )

D = durability (completed transactions should remain permanent)

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Queries

• Find all courses that “Mary” takes

• What happens behind the scene ?– Query processor figures out how to answer the

query efficiently.

SELECT C.nameFROM Students S, Takes T, Courses CWHERE S.name=“Mary” and S.ssn = T.ssn and T.cid = C.cid

SELECT C.nameFROM Students S, Takes T, Courses CWHERE S.name=“Mary” and S.ssn = T.ssn and T.cid = C.cid

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Queries, behind the scene

Imperative query execution plan:

SELECT C.nameFROM Students S, Takes T, Courses CWHERE S.name=“Mary” and S.ssn = T.ssn and T.cid = C.cid

SELECT C.nameFROM Students S, Takes T, Courses CWHERE S.name=“Mary” and S.ssn = T.ssn and T.cid = C.cid

Declarative SQL query

Students Takes

sid=sid

sname

name=“Mary”

cid=cid

Courses

The optimizer chooses the best execution plan for a query

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Database Systems

• The big commercial database vendors:– Oracle– IBM (with DB2)– Microsoft (SQL Server)– Sybase

• Some free database systems (Unix) :– Postgres– MySQL– Predator

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Databases and the Web

• Accessing databases through web interfaces– Java programming interface (JDBC)– Embedding into HTML pages (JSP)– Access through http protocol (Web Services)

• Using Web document formats for data definition and manipulation– XML, Xquery, Xpath– XML databases and messaging systems

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Database Integration

• Combining data from different databases– collection of data (wrapping)– combination of data and generation of new views on

the data (mediation)

• Problem: heterogeneity– access, representation, content

• Example revisited– http://immo.search.ch/ – http://www.swissimmo.ch

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Other Trends in Databases

• Industrial– Object-relational databases– Main memory database systems– Data warehousing and mining

• Research– Peer-to-peer data management– Stream data management– Mobile data management

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Course Outline (Details on the Web)

Part I• SQL (Chapter 6)• The relational data model (Chapter 3)• Database design (Chapters 2, 3, 7)• XML, XPath, XQueryPart II• Indexes (Chapter 13)• Transactions and Recovery (Chapter 17 - 18)Exam

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Structure

• Prerequisites: – Programming courses

– Data structures

• Work & Grading:– Homeworks (4): 0%

– Exam (like homeworks): 50%

– Project: 50% (see next) – each phase graded separately

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The Project

• Models the real data management needs of a Web company– Phase 1: Modelling and Data Acquisition– Phase 2: Data integration and Applications– Phase 3: Services

• "One can only start to appreciate database systems by actually trying to use one" (Halevy)

• Any SW/IT company will love you for these skills

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The Project – Side Effects

• Trains your soft skills– team work– deal with bugs, poor documentation, …– produce with limited time resources– project management and reporting

• Results useful for you personally– Demo:

• Project should be fun

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Practical Concerns

• New course, expect some hickups

• Important to keep time schedule

• Communication through Web

• Newsgroup

• Student committee for regular feedback (2 volunteers)

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Week Date Lecture Exercise Project Deadlines

1 11.03.2005 Introduction, Basic SQL Project Presentation

2 18.03.2005 Advanced SQL Ex. 1: SQL (on machines)

25.03.2005 Easter

01.04.2005 Easter

3 08.04.2005 Conceputal Modelling Correction Ex. 1

4 15.04.2005 Database Programming

5 22.04.2005 Functional Dependencies Ex. 2: FD and RA Phase 1

6 29.04.2005 Relational Algebra

7 06.05.2005 Introduction to XML Corr. Ex. 2 / Ex. 3: XML

8 13.05.2005 XML Query Phase 2

9 20.05.2005 Web Services Correction Ex. 3

10 27.05.2005 Concurrency Ex. 4: Transactions

11 03.06.2005 Recovery

08.06.2005 Phase 3

12 10.06.2005 Database Heterogeneity Correction Ex. 4

13 17.06.2005 Indexing

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So what is this course about, really ?

A bit of everything !• Languages: SQL, XPath, XQuery• Data modeling• Theory ! (Functional dependencies, normal

forms)• Algorithms and data structures (in the second half)• Lots of implementation and hacking for the

project• Most importantly: how to meet Real World needs