1. CS145: Intro to Database Management Systems
Lecture 1: Course Overview

2. “data is the future”
– my cab driver in
Pittsburgh

3. Outline Introduction Administrative stuff
What is a database and why do we use it?
Summary

4. Big Data Landscape… Infrastructure is Changing
New tech.
Same Principles.

5. Why should you study databases?
Mercenary: make more $$$
Startups need DB talent right away = low employee #
Massive industry…
Intellectual:
Science: data poor to data rich
No idea how to handle the data!
Fundamental ideas to/from all of CS:
systems, theory, AI, logic, stats, analysis….
Many great computer systems ideas started in DB.

6. What this course is (and is not)
Discuss fundamentals of data management
How to query databases, design databases, build applications with them.
Not how to be a DBA or how to tune Oracle 12g.
We won’t get to cover the principles of how to build database management systems. 
see 245, 345, and 346.

7. Who we are… Instructor (me) Chris Ré (sounds like Ray)
Faculty in the InfoLab
Research: theory of data processing, statistical analytics, and machine reading.
Office hours: MW in Gates 433

8. Course Assistants (CAs) !
Remember: CAs are people (students) too!

9. Joy Kim
Angela Gong
Sam Keller
Kevin McKenzie
Curran Kaushik
Vien Dinh
Duong
Michael Fitzpatrick
Firas Abuzaid
Vishnu
Sundaresan
Raven Jiang
Gina Pai
Yifei Huang
Patrick Harvey

10. Communication w/ Course Staff
Piazza,
Course mailing list,
Office hours, and
By appointment!
All are (or will be soon) listed on the course page!

11. Course Logistics cs145.stanford.edu
The Webpage contains the most up-to-date information.
cs145.stanford.edu

12. Course Elements This class is semi-flipped:
Learn from your classmates!
Some classes are flipped, some are not…
The Red F is your guide!
Attendance (10%)
Lectures or Videos per week
Videos and Slides.

13. Lectures Lecture slides cover essential material
You can (almost) always watch Jennifer instead!
Database Systems and Locking are new this time.
Try to cover same thing in many ways: Lecture, lecture notes, homework, exams (no shock)
Attendance makes your life easier…
8 lectures mandatory…must attend GUEST LECTURES!

14. All but the final assignment are due on Monday before class.
Graded Elements
Attendance (10%) – 8 Classes.
Problem Sets & EdX Questions (20%)
You can retake EdX until you get a perfect score.
Programming project (20%)
Auction base. Up now!
midterm & final exam (20%/30% of grade)
All but the final assignment are due on Monday before class.

15. What is expected from you
Attend lectures
If you don’t it’s at your own peril
Be active
Ask questions, post comments on forums
Do programming and homework projects
Start early and be honest.
Study for tests and exams.

16. Now to databases...

17. What is a DBMS? A large, integrated collection of data
Models a real-world enterprise
Entities (e.g., Students, Courses)
Relationships (e.g., Alice is enrolled in 145)
A Database Management System (DBMS) is a piece of software designed to store and manage databases

18. A Motivating, Running Example
Consider building a course management system (CMS):
students
courses
professors
who takes what
who teaches what
Entities
Relationships

19. Data models
A data model is a collection of concepts for describing data
A schema is a description of a particular collection of data, using the given data model
The relational model of data is the most widely used model today
Main Concept: relation: essentially, a table
Every relation has a schema describing types, etc.

20. “Relational databases form the bedrock of western civilization” – Bruce Lindsay, IBM Research

21. Modeling the CMS Logical Schema
Students(sid: string, name: string, gpa: float)
Courses(cid: string, cname: string, credits: int)
Enrolled(sid: string, cid: string, grade: string)
Sid
Name
Gpa
101
Bob
3.2
123
Mary
3.8
cid
cname
credits
564
564-2 4
308
417 2
Relations
sid
cid
Grade
123
564 A
Students
Courses
Enrolled

22. Other Schemata… Physical Schema: describes data layout
Relations as unordered files
Some data in sorted order (index)
Logical Schema: Previous slide
External Schema: (Views)
Course_info(cid: string, enrollment: integer)
Derived from other tables for “authorized users”
Administrators
Applications

23. NB: One of the most important reasons to use a DBMS
Data independence
Applications do not need to worry about how the data is structured and stored
Logical data independence protection from changes in the logical structure of the data
Physical data independence is protection from the physical layout changes
NB: One of the most important reasons to use a DBMS

24. Challenges with Many Users
CMS application serves 1000s+ of users
Security: Different users, different roles
Performance: Need to provide concurrent access
Consistency: Concurrency can lead to update problems
Disk/SSD access is slow, DBMS hide the latency by doing more CPU work concurrently
DBMS allows user to write programs
as if they were the only user.

25. Atomicity: An action either completes entirely or not at all
Transactions
Key concept is a transaction: an atomic sequence of db actions (reads/writes)
Transactions leave the DB in a consistent state
Users may write integrity constraints, e.g., each course is assigned to exactly one room
But, DBMS does not understand the real semantics of the data – consistency burden is still on the user!
Atomicity: An action either completes entirely or not at all

26. Scheduling concurrent transactions
DBMS ensures that execution of {T1, … Tn} is equivalent to some serial execution
Locking: Before reading or writing transaction reqs a lock from DBMS, holds until the end
Idea: If Ti writes an item x and Tj reads x then Ti, Tj conflict
only one winner gets the lock.
loser is blocked until winner finishes
What if Ti asks for X before Tj and Tj asks for Y before Ti?
Deadlock! One is aborted…

27. Ensuring Atomicity
DBMS ensures atomicity all-or-nothing property – even if a transaction crashes!
Idea: Keep a log of all writes the DB does
Write-ahead log (WAL): Before a change is made, the corresponding log entry is forced to disk
Idea: After a crash, partially executed transactions are undone using the log
NB: Thanks to WAL, if log entry not present – then its not applied to the DB

28. More details about the log
The following actions are in the log:
Ti writes an object: old value and new value
Ti commits/aborts
Log records chained by Xact ID so easy undo
Log is on “stable” storage
All log maintenance and concurrency handled transparently by DBMS

29. Friends of Databases (people made happy)
End users and DBMS vendors
Reduces cost and makes money
DB application programmers
e.g., smart webmasters
Database administrators (DBA)
Designs logical/physical schema
Handles security/authorizatino
Tuning, crash recovery, and more…
Must understand
DB internals

30. Summary of DBMS
DBMS used to maintain, query, and manage large datasets.
Provides concurrency, recovery from crashes, quick application development, integrity, and security
Key abstractions give independence
DBMS R&D is one of the broadest, most exciting fields in CS. Fact!