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Course Introduction
Introduction to Databases
Instructor: Joe BockhorstUniversity of Wisconsin - Milwaukee
First Reading Assignment
• Chapters 1 and 2 (today and part of Thursday) Chapter 13 and handout
“There's a prayer each night that I always pray:Let the data guide me through every day”
Warren Zevon
Data is Ubiquitous
• Three classes of technological advances are changing our relationship with data:
• More storage space– allows us to keep more data
• Faster processor (and memory) speeds– allows us to access and process more data
• Different “sensors”– allows us to access new kinds of data
http://en.wikipedia.org/wiki/Hard_disk
Microarrays – An Example of aNew Sensing Technology
The color of each spot represents the activity level of a gene under some experimental condition
10 000s of spots on a single chip
A microarray
Other Data Examples
• Airline flight management system• Financial data• Commercial store (eg, WalMart) data• Department of Motor Vehicles• Surveillance video• University student records• Baseball results• Web sites• Medical records• ...
Effectively Data Management is Essential
• Organizations need their data to be an asset• Given:
the amount of data available to store&costs to manage data (hardware, software, labor)
• Ineffective policies can make an organization’s data a liability
Database Management System (DBMS)
• DBMS is:– A collection of software programs– General purpose
• DBMS enables users to:– Define DB– Construct DB– Change (or update) DB– Ask questions about the data in DB– Share DB
• DBMS maintains the integrity of DB
Some RDBM Systems
Commercial SystemsOracle ($$$$)DB2 (IBM) ($$$)SQL Server (Microsoft) ($$)
Open Source SystemsPostgreSQLMySQL
Source: International Data Corporation
Main Goals of this Course
• To understand how to use a DBMS– How to create DB, data models, SQL,...
• To understand how a DBMS works– Physical properties of disks and files, software to
manage reading and writing to disk, implementation of algorithms to answer user queries,...
catalog
Databases are self-describing: catalog describes the structure of the data stored in the DB
Example: Internet Movie Database (IMDB)
Building a DB:construct a conceptual model
movie person
acts in
director of
title release date name birthdate
rolerole type
• A conceptual model identifies entities and relationships
MN
N1
entity attribute relationship
Building a DB:Define DB Schema
• A schema describes DB using data modelsupported by DMBS (eg, relational model)
• RDBMS – DBMS that supports relational model
Rating DirectorTitleMID
BdayNamePID
RtypeRolePIDMID
MOVIE
PERSON
ACTS_IN
A Schema Diagram for “University” DB(from the textbook)
tables
columns
Building a DB:Describe Physical Data Model
• PDM indicates how data is organized on disk• Includes description of access paths or indexes
– Example: store “Movie” table with records ordered by MID and construct an index on the “Title” attribute
1 The Big Lebowski R 99
2 Star Wars PG 16
270 The Big Chill PG 3
The Big Chill
The Big Lebowski
File of records of the MOVIE tableIndex on Title column
Building a DB:Populate DB
PGRRating
...29Star Wars272The Big Lebowski1DirectorTitleMID
...7/13/42Harrison Ford212/4/49Jeff Daniels1BdayNamePID
...
CO_STARHan Solo22
STARThe Dude11
RtypeRolePIDMID
MOVIE
PERSONACTS_IN
Set initial records of the DB
Querying The Database
• Most RDBMS allow users to query the database using SQL (structured query language)
• Example: get cast of “The Big Lebowski”
SELECT Name, Role, RtypeFROM PERSON, ACTS_INWHERE MID = ‘1’ AND PERSON.PID == ACTS_IN.PID
Building the Application Program
Implementing Queries
• “Relational Algebra” is a mathematical way to describe operations on relational data
• SQL queries correspond to sequence of relational algebra operations– The previous query requires a join operation
between person and acts_in
• Query Optimization involves finding a good order to carry out operations
• Operator implementation
Managing Physical Data Storage
• RDBMS maintains database (and meta-data) on non-volatile storage (hard disks)
• Physical design impacts RDBMS performance
• Example: The time to answer a query such as What is the MID of “The Big Lebowski” can be greatly reduced if an index of Title column is maintained for the Movie table.
Maintaining Integrity of the Database
• Concurrent users– Multiple users may attempt to update simultaneously
• Security– Preventing unauthorized access
• System failures– If lightening strikes during an update the DB must
able to be recovered
Summary of Topics
• Conceptual modeling• Logical Modeling• Querying the DB• Building applications • Implementing Queries• Managing hardware• Maintaining Integrity
how to use DBMS
how a DBMS works
Control Abstraction
Query Optimization
Relational Operators
Files and Access Methods
Buffer Management
Disk Space Management
DB
Application Program
User
DBMS
Each layer need not know (or care) how other layers are implemented
Data Abstraction
Each layer need not know how other layers organize data
Why Use DBMS?
• Program Data Independence• Controlling redundancy• Providing backup and recovery• Efficient query processing• Others: see Section 1.6
Why not to use a DBMS?
• Consider custom software if DBMS overhead (cost, complexity, performance) is unnecessary– Example: single user of fixed dataset
Schemas and Instances
• A schema describes a database– RDBMS typically store schemas in the catalog
• The actual data in the DB at a particular time is the database state– The current set of all instances in the DB
People who work with DBMSs
• Database Administrator DBA– Maintains databases, DBMS and related software– [avg salary* $76k]
• Application Programmers– Software engineers (developers) that build software
solutions for end users that access DBMS• End Users
– Example: bank teller uses “canned transactions”• DBMS designers and implementers
– Example: Oracle developers
*source: payscale.com, 2007