1 Introduction to Information Systems SSC, Semester 6 Lecture 01

2 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)

3 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

4 Textbook Main textbook: Databases and Transaction Processing, An application-oriented approach Philip M. Lewis, Arthur Bernstein, Michael Kifer, Addison-Wesley 2002.

5 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)

6 Material on the Web SQL Intro SQL for Web Nerds, by Philip Greenspun, Java Technology java.sun.com WWW Technology

7 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 – s/cse444/ s/cse444/ – /4.AlonLevy.pdfhttp:// /4.AlonLevy.pdf

8 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

9 Outline for Today’s Lecture Overview of database systems Course Outline First Steps in SQL

10 What is behind this Web Site? Search on a large database Specify search conditions Many users Updates Access through a web interface

11 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)

12 Where are RDBMS used ? Backend for traditional “database” applications –EPFL administration Backend for large Websites –Immosearch Backend for Web services –Amazon

13 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

14 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

15 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:

16 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 !

17 Enters a DBMS Data files Database server (someone else’s C program) Applications connection (ODBC, JDBC) “Two tier system” or “client-server”

18 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)

19 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 Students VALUES(‘Charles’, ‘ ’, ‘undergraduate’).. INSERT INTO Students VALUES(‘Charles’, ‘ ’, ‘undergraduate’)..

20 How the Programmer Sees the DBMS Tables: Still implemented as files, but behind the scenes can be quite complex Students:Takes: Courses: “data independence” = separate logical view from physical implementation

21 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

22 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)

23 Queries Find all courses that “Mary” takes What happens behind the scene ? –Query processor figures out how to answer the query efficiently. SELECT C.name FROM Students S, Takes T, Courses C WHERE S.name=“Mary” and S.ssn = T.ssn and T.cid = C.cid

24 Queries, behind the scene Imperative query execution plan: SELECT C.name FROM Students S, Takes T, Courses C WHERE S.name=“Mary” and S.ssn = T.ssn and T.cid = C.cid SELECT C.name FROM Students S, Takes T, Courses C WHERE 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

25 Database Systems The big commercial database vendors: –Oracle –IBM (with DB2) –Microsoft (SQL Server) –Sybase Some free database systems (Unix) : –Postgres –MySQL –Predator

26 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

27 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 – –

28 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

29 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, XQuery Part II Indexes (Chapter 13) Transactions and Recovery (Chapter ) Exam

30 Structure Prerequisites: –Programming courses –Data structures Work & Grading: –Homeworks (4): 0% –Exam (like homeworks): 50% –Project: 50% (see next) – each phase graded separately

31 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

32 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

33 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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35 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