Post on 12-Jan-2016
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Databases and Data Representation
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Databases and Data Representation
Database Management System (DBMS) Provides efficient, convenient, and safe multi-
user storage of and access to massive amounts of persistent data
Provides a programming interface that allows a user or program too - Create new databases and specify their structureo - Query and modify the data
Early DBMSs were ad hoc, with no two the same Now one approach predominates: relational
databases and SQL (Structured Query Language)
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Databases
A "relation" is a table of data
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
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Databases
The columns are known as "attributes"
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
LectID Name Course Students
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Databases
The rows are called "tuples"
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
LectID Name Course Students
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Databases
It is allowable for some values to be missing
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01
4 Josh CS120-02 23
LectID Name Course Students
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Databases
We can add, remove, or update tuples
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
LectID Name Course Students
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Databases
Each attribute has an underlying domain, or data type
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
LectID Name Course Students
int string string int
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Databases
The structure of the table is referred to as its schemao Lecturers(LectID, Name, Course, Students)
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
LectID Name Course Students
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Primary Key
Every table must have a primary keyo No two tuples can have the same LectID
o LectID cannot be null
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
LectID Name Course Students
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Tables
Suppose that we want to add data about lecturers offices
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
Name Course StudentsLectID
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Tables
But suppose that lecturers can have more than one office.
We can’t add additional rows for the same lecturers without violating the primary key constraint, so we use another table.
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
Name Course StudentsLectID Building Room
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Multiple Tables
Solution: Add a new table
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
Name Course StudentsLectID
Shereen Strain 203C
Josh Marsh 324
Josh Strain 202
Doug Strain 201
Building Room
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Relationships
Better to store LectID
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
Name Course StudentsLectID
1 Strain 203C
4 Marsh 324
4 Strain 202
2 Strain 201
Building RoomLectID
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Relationships
Better to store LectID
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
Name Course StudentsLectID
1 1 Strain 203C
2 4 Marsh 324
3 4 Strain 202
4 2 Strain 201
Building RoomLectID
Foreign key
Primary key
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SQL Queries
SELECT returns tuples that satisfy some condition
SELECT Name, Course FROM Lecturers WHERE Students > 15
1 Shereen CS360-01 12
2 Doug CS300-01 11
3 Chris CS445-01 15
4 Josh CS120-02 23
5 Mike CS120-02 19
Name Course StudentsLectID
Josh CS120-02
Mike CS120-01
Name Course
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SQL Queries
SELECT *
FROM Lecturers
WHERE Students > 15
Attributes
Relations
Tuples
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SQL Queries
SELECT *
FROM Lecturers
WHERE Students > 15
OR Name = ‘Shereen’
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SQL Queries
Wildcards:o % matches any number of characters
o _ matches any single character
o [] matches any single character in set or range
o [^] matches any single character not in set or range
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Database Management Systems
Many examples of DBMSso Oracle
o SQL Server
o MySQL http://dev.mysql.com/