Download DB1 English - Introduction

Databases
Content
What is a database?
What is a relational database?
Concept and terminology
An introduction by example
Relational algebra: the key of success
Introduction to SQL (Structured Query Language)
Teaching
Lectures (5 h), Course work (4 h), Practical work (6 h)
Written test (1 h 30)
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Introduction
A database is a collection of related data
name, phone number, address of people you know
A database is a logically consistent collection of data with
some inherent meaning
A database is designed, built and populated with data for a
specific purpose
A database can be of any size and of varying complexity
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From Files to Databases
A file is a set of objects of the same type stored on a physical
support.
Information system example: Social Network
Members
Name
Nickname
Email
Password
Jane's friends
Dan's friends
Jane's friends
Dan's friends
Name
Nickname
Email
Relationship
Name
Nickname
Email
Relationship
Name
Nickname
Email
James Bond
jb007
Clark Kent
superman
[email protected]
coworker
Lois Lane
lolo
lola123
[email protected]
coworker
Tarzan
kikoo68
[email protected]
engaged
Name
Nickname
doedoe
[email protected]
Relationship
Email
[email protected]
friend
Relationship
brother
Bill Gates
bill_gates
[email protected]
boss
Clark Kent
superman
[email protected]
friend
[email protected]
friend
Lois Lane
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lola123
Using Files?
Several files with the same data:
Redundancy of information
Volume, access time, validity, duplicates
Difficult to update
Change email in all files
Difficult to retrieve data
Problem for finding information, reading (e.g., how can one
read the file when it is being updated), etc.
File
Programme
The application depends on
the way the data is stored
Report
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Beyond Files?
Make programmes independant from the way data is stored
Data Base Management System (DBMS)
DB1
DB2
DBn
...
One DBMS
DBMS
Ap1
Ap2
Many databases
Apk
Many applications
Can access many different databases
The structure of data is stored in the DBMS directory
separately from the access programs
Concrete data storage is “hidden”
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What is a DBMS?
A programme that allows users to create and maintain a
database
Defining: data types (numbers, text, dates, etc.)
Constructing: populating the database
Manipulating: updating, inserting, deleting (e.g.,
add/remove a friend)
Retrieving data according to criteria (e.g., “give me all my
friends that have developped a Facebook application and
that are less than 18 year old”)
Manage access rights (e.g., not all users can access
passwords)
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Role of a DBMS
Avoiding redundancy
Sharing of data
Restricting unauthorized accesses
Enforcing integrity constraints
Providing multiple interfaces
Providing backup and recovery
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Role of a DBMS (contd.)
Avoiding redundancy
Redundant data mean:
Duplication of effort
Wasted storage space
Possible inconsistency during updates (one has to update all
the duplicates)
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Role of a DBMS (contd.)
Sharing of data
Multi-user context (sometimes ~1,000 users at the same
time)
There must be concurrency control
What if two people try to update the same data?
Ensure the result of the updates is correct
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Role of a DBMS (contd.)
Restricting unauthorized accesses
Privacy of data (postal address, birthday, etc)
Security of sensitive data (passwords, confidential data, etc)
Some users are not authorized to access all information in the
database
Some users are allowed only to retrieve data whereas others
are allowed to both retrieve and update
Students: read their own marks after the exams
Teachers: read and update all marks for their own students
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Role of a DBMS (contd.)
Enforcing integrity constraints
To ensure consistency of data:
Specify a data type for each data item
The birthday must be a date before the current day
The value of the name data item must be a string of no more
than 30 characters
Referential integrity
A record in one file must be related to records in other files
(e.g., a friend must be an existing member of the social
network)
Uniqueness constraint
An identifier must be unique (e.g., the login)
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Role of a DBMS (contd.)
Providing multiple interfaces
Menu-driven interfaces for newbies
First computer-based practical works
Query language for casual computer scientists (SQL)
Second computer-based practical works
Programming language interfaces for programmers
Beyond the scope of this course
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Role of a DBMS (contd.)
Providing backup and recovery
For many companies, data is vital: they must not lose the
data!
There are many ways to lose data
Hardware crashes
Programme bugs
Viruses
Hackers
Earthquakes, floods, hurricane, tornado...
Facilities for recovering from failures
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Some relational DBMS
Toy DBMSs
Access (Microsoft)
Base (OpenOffice, free and open source)
Perfect for your stamp collection
Medium DBMSs
MySQL
Good for a small and medium size enterprise
Professional DBMSs
Oracle
Large and very large databases
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Relational Databases
“All is table”
1 table == 1 relation
e.g., table User is a relation between a login, a password, an
email, a name, etc... (n-ary relations)
Created by Edgar CODD (late 1960s)
Set of operations on tables (relational algebra)
In order to combine information from different tables
Language to query the database (SQL)
To retrieve information from the tables
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Tables / Relations
Song(Title, Artist, Album, Release-date, Composer)
Song
Title
Artist
Album
Aphex Twin
Drukqs
...
Cocorosie
Noah's Ark
...
Christmas Song
Mogwai
EP + 2
...
I Luv The Valley OH!
Xiu Xiu
Fabulous Muscles
...
Vordhosbn
Beautiful Boyz
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...
Tables / Relations
Song(Title, Artist, Album, Release-date, Composer)
1 column == 1 attribute
Song
Title
Artist
Album
Aphex Twin
Drukqs
...
Cocorosie
Noah's Ark
...
Christmas Song
Mogwai
EP + 2
...
I Luv The Valley OH!
Xiu Xiu
Fabulous Muscles
...
Vordhosbn
Beautiful Boyz
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...
Tables / Relations
Song(Title, Artist, Album, Release-date, Composer)
Song
Title
Artist
Album
Aphex Twin
Drukqs
...
Cocorosie
Noah's Ark
...
Christmas Song
Mogwai
EP + 2
...
I Luv The Valley OH!
Xiu Xiu
Fabulous Muscles
...
Vordhosbn
Beautiful Boyz
1 row == 1 tuple
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...
Concepts of relational databases (1)
A table or relation: a set of rows
Think n-ary relations
A row is called tuple1: set of values about a thing (object,
person, events, etc)
In table Song, each row represents fact about a particular
song
All rows have the same structure
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The term “tuple” comes from the sequence quadruple, quintuple, sextuple,
septuple, octuple, etc.
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Concepts of relational databases (2)
A column is the set of values concerning a property
All values in a column are of the same data type (e.g.,
integer, date, character string, text)
A column name is called an attribute (or a field).
The attribute Release-date represents the song's release date
A column can have an unknown value (Null)
A column could be an identifier (e.g., Song-ID) to avoid
ambiguity in naming
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Concepts of relational databases (3)
The data type describing the type of values that appears in
each column is called a domain
A domain is a set of atomic values
e.g., release date: set of dates (not including day time)
number of tracks: a value between 1 and 99 (the limit for
an audio CD)
Null values represent attributes whose values are unknown
or do not exist for some tuples
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Concepts of relational databases (4)
A relation schema defines the attributes of a table
A relation schema R is denoted: R(A1, A2,…, An)
R is the name of the table, A1, A2,…, An are the attributes
e.g., Song(Title, Artist, Album, Release-date, Composer)
Each tuple t is an ordered list of n values
t = (v1, v2, …, vn)
("Vordhosbn", "Aphex Twin", "Drukqs", 2001, "R. D. James")
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Concepts of relational databases (5)
One of the attributes, or the association of several attributes,
has the role of identifying a tuple uniquely. It is called the
primary key of the table. It must not be Null
e.g., social security number, car plate, student number
Song(SongID, Title, Artist,...)
The same value for a primary key cannot be used in two
different tuples
The key allows the access to a unique row
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Concepts of relational databases (6)
A foreign key is a key which is referenced in another table
Song(SongID, Title, ArtistID, AlbumID ...)
Artist(ArtistID, ArtistName, RealName, Birthday, ...)
Album(AlbumID, Title, ReleaseDate, Label, ...)
Referential constraints: the value of a foreign key in a
table should exist in the table in which this attribute is a key
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