CS3431 –
Database Systems I
Introduction
Instructor: Murali Mani
mmani@cs.wpi.edu
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What is a Database System?
• Database:
a large collection of related data
usually too large to fit in computer memory at once
usually data is important for the application
usually many users may need fast access to data
Focus: information, rather than computation
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Database Applications
Have you ever used a database application?
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E-commerce: books etc at Amazon, B&N
Banks -- your valuable $$ and ATM transactions
Airlines – manage flights to get you places
Universities – manage student enrollment
GIS (Maps) – find restaurants closest to WPI
WWW (World Wide Web) – blobs, wikis, etc. ?
Bio-informatics (genome data)
Datasets increasing in diversity
and volume everywhere !!!
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Example Database : Relational
Tabular View of Data: Airline System
Flight
flightNo
start
destination
miles
101
BOS
LAX
3000
102
PVD
LAX
2900
Passenger
FlewIn
Tabular
pName
ffNumber
DoB
milesEarned
Joe
1001
1980
12000
Mary
1002
1981
11000
flightNo
ffNumber
date
101
1001
Jan 4
102
1002
Jan 5
view of data is called Relational Model
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Basic Terminology
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Data Model:
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Schema:
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Describes “structures” for a particular application, using the
given data model
Database :
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A collection of “concepts” used for describing data
Collection of actual data that conforms to given schema
Database Management System :
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Software that allows us to create, use and maintain a
database (conforming to given model).
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Relational Data Models
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The relational model of data
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The most widely used model today.
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Main concept: relation, basically a table with
rows and columns.
Every relation has a schema, which describes
the columns, or fields.
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Levels of Abstraction
• External schema (view) -describes how users see the
data
• Logical schema –
describes the logical
structures used
View1
View2
View3
Logical Schema
Physical Schema
disk
• Physical schema -describes files and indexes
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Levels of Abstraction: Example
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Logical (Conceptual) Schema:
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Physical Schema
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Flight, Passenger, FlewIn tables
Flight table stored as a sorted file
Index on flightNo attribute for Flight relation
Views ( External Schema )
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NoOfPassengers (flightNo, date, numPassengers)
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Why use DBMS, and not files?
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Data independence (robustness under change)
Efficient access even on huge data sets
Reduced application development time
Data integrity ensures consistency of data even
with multiple users
Recovery from crashes, security, etc.
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Who use databases?
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End users
DB application programmers
Database Administrators
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Database design
Security, Authorization
Data availability, crash recovery
Database tuning (for performance)
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Summary : Why study DBMS?
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Need to process large amounts of data increasing
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Video, WWW, computer games, geographic
information systems (GIS), genome data, digital
libraries, etc.
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DB administrators and programmers hold
rewarding jobs.
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DBMS research is one of the most exciting areas in
Computer Science !!
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Introductory Material
Sets, Relations and Functions
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Sets
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Unordered collection of objects
Characteristics
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Unordered
No duplicates (no object appears more than
once in a set)
Eg: Set of passengers, set of flights
Recall the main set operations
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Union, intersection, complement
Check subset
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Relations
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Given multiple sets A1, A2, …, An, a relation is a
set of n-tuples of the form (a11, a12, …, a1n),
where a11 is an element of A1, a12 is an element
of A2, and so on.
Eg: suppose the set of course = {DB1, DB2}, the
set of TAs = {Hong, Song}, then a relation
between these two sets could be
{(DB1, Hong), (DB1, Song), (DB2, Hong)}
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Functions
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Given two sets A, B, a function f from A to B is
denoted as f: A  B. This maps any value of A to
one value of B.
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Eg: consider function from faculty members to depts
{(Mike Gennert  CS), (Peter Hansen  Humanities)}
Characteristics
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A is called domain
B is called range
No value of A can map to multiple B’s.
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Functions
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Injection (one to one):
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Surjections (onto)
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No 2 values in A map to the same B
Eg: set of Husbands  set of wives
Every value in B has at least 1 value in A that
maps to it
Bijections
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One to one and onto
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