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CS3431 –Database Systems I

Introduction

Instructor: Murali Mani mmani@cs.wpi.edu

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What is a Database System?

usually too large to fit in computer memory at onceusually data is important for the applicationusually many users may need fast access to data

• Database: a large collection of related data

Focus: information, rather than computation

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Database Applications

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)

Have you ever used a database application?

Datasets increasing in diversity and volume everywhere !!!

?

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Example Database : Relational

Tabular View of Data: Airline System

Flight

Passenger

flightNo start destination miles

101 BOS LAX 3000

102 PVD LAX 2900

pName ffNumber DoB milesEarned

Joe 1001 1980 12000

Mary 1002 1981 11000

flightNo ffNumber date

101 1001 Jan 4

102 1002 Jan 5

FlewIn

Tabular view of data is called Relational Model

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Basic Terminology

Data Model: A collection of “concepts” used for describing data

Schema: Describes “structures” for a particular application, using the

given data model

Database : Collection of actual data that conforms to given schema

Database Management System : Software that allows us to create, use and maintain a

database (conforming to given model).

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Relational Data Models

The relational model of data The most widely used model today.

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

View1 View3View2

Logical Schema

Physical Schema

disk

• External schema (view) --describes how users see the data

• Logical schema – describes the logical structures used

• Physical schema -- describes files and indexes

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Levels of Abstraction: Example

Logical (Conceptual) Schema: Flight, Passenger, FlewIn tables

Physical Schema Flight table stored as a sorted file Index on flightNo attribute for Flight relation

Views ( External Schema ) NoOfPassengers (flightNo, date,

numPassengers)

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Why use DBMS, and not files?

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?

End users DB application programmers Database Administrators

Database design Security, Authorization Data availability, crash recovery Database tuning (for performance)

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Summary : Why study DBMS?

Need to process large amounts of data increasing Video, WWW, computer games, geographic

information systems (GIS), genome data, digital libraries, etc.

DB administrators and programmers hold rewarding jobs.

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

Unordered collection of objects Characteristics

Unordered No duplicates (no object appears more than

once in a set) Eg: Set of passengers, set of flights Recall the main set operations

Union, intersection, complement Check subset

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Relations

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

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. Eg: consider function from faculty members to depts {(Mike Gennert CS), (Peter Hansen Humanities)}

Characteristics A is called domain B is called range No value of A can map to multiple B’s.

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Functions

Injection (one to one): No 2 values in A map to the same B Eg: set of Husbands set of wives

Surjections (onto) Every value in B has at least 1 value in A that

maps to it Bijections

One to one and onto