lecture1a introduction to databases

INTRODUCTION TO DATABASES

What is a database (DB)?

What is a database (DB)?• A collection of data

• Needs to be stored• Needs to be retrieved (possibly only parts) at some later moment• Might need to be updated/modified at some later moment

What is a database-management system (DBMS)?

• A collection of data (ie, database) and• A set of programs to access these data

• Read, add, delete, update records or parts of records• Often “invisible” to end-users of a database

Examples where databases are used…

• What are some real-life applications of databases?

Examples where databases are used…

• University:• List of instructors, their department, classes, taught, salary,

address• List of students, major, classes taken, GPA, address• List of classes at the university, room, time

• Airline:• List and status of airplanes, pilots, support personnel• List and status of flights

• Hospital:• List of doctors, their specialization, their availability• List of patients and their health history

We interact with a database “daily” (without even realizing it)• Register for a class• Search a list of movies playing in a nearby cinema• Look current weather conditions• Check Facebook news feed• Create LinkedIn profile• Add a friend on Google+

A practical example: Netflix• An online “store” of movies and TV shows• A person pays monthly subscription to “rent” any amount

of movies/TV shows that are available• Netflix recommends movies/TV shows based on history of

usage by a person

TASK:• Let’s come up with a list of information that needs to be

stored• Ignore HR department and personnel working for Netflix

Netflix: info to store• User:

• Username and password• Real name (first name and last name)• Credit card info (or bank account info)• Account is active or not• History of movies/TV shows watched• Recommendations ???

• Movie/TV show:• It’s a movie or a TV show• Title• Genre• Director(s)• Main actor(s)• Year produced• Oscar recipient/nomination

Different methods to store information

• Pen and paper• Microsoft excel sheet• File-processing system (supported by operating system)• Database

Advantages of DB• Can store large amount of information in a very organized

way.• Data redundancy and inconsistency can be removed.• Easy to access data.• All data is at the “same” place.• Integrity (ie, consistency constraints can be imposed).• Atomicity (ie, multiple operations are considered as one).• Concurrent access is not a problem.• No security problems (ie, different types of users can be

given access to different data).

We will revisit each of these topics.

DB is “a set of tables”• User table:Username

Password Real name

Credit card

Active account

History Recommendations

Jsmith3 Pass1 John A. Smith

xxxxx Y NCIS, 12 Years of Slave

Law and Order

Mrayn Pass2 Mary Raynolds

xxxxx Y Hobbit, Hunger Games

gomezs Pass3 Stan Gomez

xxxxx N

DB is “a set of tables”• User table:

• Any issues/concerns/difficulties?

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

• Username should be unique!!! -> not a problem, but we need to have that constraint programmed.

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

• Password should satisfy some predetermined conditions not a problem, but needs to be programmed.

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

• Real name: maybe we want to split it into 2 columns: first name and last name.

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

• Credit card: we need lots of info: number, expiration date, security number -> maybe we need more than one field.

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

• Credit card: what if we allowed credit card info or bank account? -> Different fields for bank account -> new table.

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

DB is “a set of tables”• User table:Username

Password Real name

Payment Active account

Credit card

Y NCIS, 12 Years of Slave

Law and Order

Bank account

Y Hobbit, Hunger Games

Bank account

Payment tables• Credit card:

• Bank account:

Credit card number

Expiration date Security number

9867432554321223

12/2017 543

Routing number Account number

1231231231 9765432134

4343434343 7543009990

• Bank account:

• Any issues???

Credit card number

Expiration date Security number

9867432554321223

12/2017 543

Routing number Account number

1231231231 9765432134

4343434343 7543009990

• Bank account:

Username Credit card number

Expiration date

Security number

Jsmith3 9867432554321223

12/2017 543

Username Routing number Account numberMrayn 1231231231 9765432134

gomezs 4343434343 7543009990

• Bank account:

• Could have we used first and last name? Address?

Username Credit card number

Expiration date

Security number

Jsmith3 9867432554321223

12/2017 543

Username Routing number Account numberMrayn 1231231231 9765432134

gomezs 4343434343 7543009990

• History: multiple titles in the same field…hard to distinguish between title, hard to search -> new table

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

History table

Username Showjsmith3 12 Years of Slave

jsmith3 NCIS

Mrayn Hobbit

Mrayn Hunger Games

• Recommendations: multiple titles in the same field…hard to distinguish between title, hard to search -> new table

Username

Password Real name

Credit card

Active account

Law and Order

xxxxx N

way.• Data redundancy and inconsistency can be removed.• Easy to access data.• All data is at the “same” place.• Integrity (ie, consistency constraints can be imposed).• Atomicity (ie, multiple operations are considered as one).• Concurrent access is not a problem.• No security problems (ie, different types of users can be

given access to different data).

way• There is no limit on number of tables in a DB.• There is no limit on number of columns and rows in a DB.We can store large amount of data.We can organize data anyway we want.

Advantages of DB• Data redundancy and inconsistency can be removed.

• Data redundancy = store same information in multiple places. • Eg., we have a table for movies and a table for TV shows, and for each

of them, we have separate list of customers (username, password, first name, last name, etc.) this is unnecessary redundancy bad DB design

• Inconsistency = pieces of data do not agree.• What if a person changes her name? Updates might have to be made in

both lists of customers, but the customer might remember to do it only at one place. Creates inconsistency.

Advantages of DB• Easy to access data.

• It is easy to search data by any value in any column in any table (if DB is designed well).• Eg., A person forgot username and password, it is easy to search by

first name and last name columns (at the same time), and then ask for additional info (address, email…) to verify the correct person is found or to filter out wrong records if multiple records have same first and last names.

• We can search for all customers who saw a particular movie (this is another reason why we might want to have history as a separate table and each movie seen by a person on a separate line).

• We can search for all customers who have had membership for more than one year. Or can we?

Advantages of DB• All data is at the “same” place.

• There are no different files or folders to search.• It seems as everything is stored together.

Advantages of DB• Integrity (ie, consistency constraints can be imposed).

• Eg., username should satisfy certain constraints (at least 6 characters long, must be unique…).

• It is easy to impose these constraints in a DB. • It is programmer once even though username might be used in

multiple tables.

Advantages of DB• Atomicity = multiple operations are considered as one

• When credit card is charged, the customer must be given an “active” status. What if something happens (ie, system failure) between charging credit card and setting customer’s status to “active”?

Advantages of DB• Concurrent access is not a problem.

• Multiple users may access DB at the same time.

Advantages of DB• No security problems (ie, different types of users can be

given access to different data).• Eg., Users are not allowed to update any record in movies table,

but they can search this table.• Eg., On the other hand, Netflix workers can update movies table.

DB terminology

• DB schema = DB design• DB instance = a collection of information stored in DB at

the moment

• Data-definition language (DDL) = language used to specify DB schema

• Data-manipulation language (DML) = language used to manipulate (add, delete, update) information in DB• It changes DB instance

DB schema• How many tables?

• Each table has a name. • It represent an “object”.

• How many columns in each table?• Each column is an attribute of the object it represents.• Each column saves data of a particular type: char(50), bigint(30),

date• How do we differentiate each record in a table?

• By a unique key. DB schema defines a key for each table.• There might be foreign keys present in some tables.

Data-definition language• Eg.,CREATE TABLE user

(username VARCHAR(20) NOT NULL, first_name VARCHAR(15) NOT NULL,

last_name VARCHAR(15) NOT NULL, account_active CHAR(1), date_enrolled DATE, number_movies_watched BIGINT(30), PRIMARY KEY username);

• SQL (Structured Query Language) for DDL

Data-definition language• Defines/ensures:

• Domain constraints• Must exist for each attribute• Eg., bigint, varchar

• Referential integrity• Eg., Each movie that show in a user’s history mist exist in movies table.

• Assertions• Any domain constraint is an assertion• Any referential integrity is an assertion• Other assertions exist

• Eg., password must satisfy some criteria (at least 6 characters long, contain at least one letter and one digit…)

• Authorization• Read authorization in movies table for users• Update authorization in movies for administrators

Data-manipulation language• SQL • Used to

• Retrieve data from DB• Insert new info in DB• Delete info from DB• Modify a piece of info in DB

• Eg., SELECT user.first_name,user.last_name FROM user WHERE user.active=“Y”;

DB design• DB has lots of advantage, but it has to be designed well to use

these advantages.• Several steps in DB design:

• Understand requirements• What information will be saved?

• Users (username, password…)• How information will be used?

• Customers: search movies by title, actor, genre,…• What additional “functionalities” might be required later?

• Allow payments by bank account• Conceptual design

• Describe data and relationships among pieces of information.• Types of data (char, int, date…)• Can one user have multiple movies listed in history? Should history be a table on its own?

• Physical design• Translate conceptual design into DB

Understanding requirements• Lots of conversations between DB developers (ie., tech

people) and business people of the company or end-users.

• Usually several iterations happening between all parties involved to clarify details. Some of them happen after conceptual design has already started.

Conceptual design• The most important and hardest part of DB design.• Two common methods:

• Entity-relationship (E-R) model• Normalization

E-R model• Graphical representation of DB model.

• Unified Modeling Language (UML) is most commonly used for this representation.

• Entity = an “object”. • Represented by a rectangle.• It has entity name (on top) and a set of attributes.

• Relationship = relationship between two entities.• Represented by a diamond.• Relationship name is written inside the diamond.• It connects two entities.• It might contain cardinalities.

E-R modeluserUsernamePasswordFirst nameLast nameAddressEmailActive account

Credit cardNumberExpiration dateSecurity code

HistoryMovie titleDate watched

Belongs to

Used by

Normalization• A set of algorithms to make sure that data are

represented in “normal form”.• Normal form:

• No redundancy• Eg., We could have all TV show information in history rather than having

a separate table for TV show

but we would repeat all this info for every person who watches NCIS.What if director changes at some moment or a new actor is added?

usename title actors director genreJsmith3 NCIA MH,PP,SS Bellisario drama

Normalization• Normal form (con’t):

• No inability to represent information• In a previous example (if we didn’t have separate table for TV shows),

what would happen if there is a TV show that noone has watched yet (eg., a new TV show)? The info would not be able to be stored anywhere.

Physical design• Pretty simple for a DB expert.• Translation from detailed human language to SQL or other

DB language.

Who interacts with a DB?• DB administrators

• They create/update/manage DB• Sophisticated (tech) users

• They “analyze” data• They use SQL-type language to directly interact with DB

• Naïve (non-tech) end-users (eg., Netflix customers)• They search DB• They use application programing interface to interact with DB

• Often via web

• Application programmers• They create/program application programming interface for naïve

end-user

Types of DBs• Relational DB• Object-based data models

• Developed to suit better object-oriented programming languages.• Extension of E-R model to allow for structured and collection types,

encapsulation, inheritance…• Semistructured data models

• Allows specification of data where a data item might have different set of attributes for different records.

• XML language

lecture1a introduction to databases

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