Transcript relational database

Chapter 14
Databases
OBJECTIVES
After reading this chapter, the reader should
be able to:
Understand a DBMS and define its components.
Understand the architecture of a DBMS and its levels.
Distinguish between different database models.
Understand the concept of relational database operations
on a relation.
Use Structured Query Language (SQL) to define simple
relations.
14.1
DATABASE
MANAGEMENT
SYSTEM
DBMS

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Database – a collection of data that is logically
coherent.
DBMS – Database Management System
 defines,
creates, and maintains a database.
 Allows users controlled access to data in the database.
 A combination of 5 components:
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Hardware
Software
Data
Users
Procedures
Figure 14-1
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DBMS components
Hardware –
the physical computer system that allows physical access to data.

Software –
the actual program that allows users to access, maintain, and update
physical data.
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Data – stored physically on the storage devices
Users –


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End users - Normal user and DBA (Database Administrator)
Application programs
Procedures –
a set of rules that should be clearly defined and followed by the users.
14.2
ARCHITECTURE
Figure 14-2
Database
architecture
Architecture

Internal level –
 Determines
where data are actually stored on the
storage device.
 Low-level access method

Conceptual level –
 Defines
the logical view of the data
 The main functions of DBMS are in this level.

External level –
 Interacts
directly with the user.
 Change the data coming from the conceptual level to
a format and view that are familiar to the users.
14.3
DATABASE
MODELS
Database models

A database model
 defines
the logical design of data.
 Describes the relationships between different
parts of data.

3 models
 Hierarchical
model
 Network model
 Relational model
Figure 14-3
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Hierarchical model
Data are organized as an upside down tree.
Each entity has only one parent but can have
several children.
Figure 14-4
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Network model
The entities are organized in a graph.
Some entities can be accessed through several paths.
Figure 14-5
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Relational model
Data are organized in two-dimensional tables
called relations.
The tables are related to each other.
The most popular model.
14.4
RELATIONAL
MODEL
Relational model

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RDBMS (Relational Database Management System)
external view
 The
data are represented as a set of relations.
 A relation is a two-dimensional table.

This doesn’t mean that data are stored as tables;
the physical storage of the data is independent of
the way the data are logically organized.
Figure 14-6
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Relation
Name – each relation in a relational database should have a name that is
unique among other relations.
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Attribute – each column in a relation.

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The degree of the relation – the total number of attributes for a relation.
Tuple – each row in a relation.

The cardinality of the relation – the total number of rows in a relation.
14.5
OPERATIONS
ON
RELATIONS
Operations on relations
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In a relational database, we can define several operations
to create new relations out of the existing ones.
Basic operations:

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Insert
Delete
Update
Select
Project
Join
Union
Intersection
Difference
Figure 14-7
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Insert operation
An unary operation.
Insert a new tuple into the relation.
Figure 14-8
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Delete operation
An unary operation.
Delete a tuple defined by a criterion from the relation.
Figure 14-9
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Update operation
An unary operation.
Changes the value of some attributes of a tuple.
Figure 14-10
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Select operation
An unary operation.
It is applied to one single relation and creates another
relation.
The tuples in the resulting relation are a subset of the tuples
in the original relation.
Use some criteria to select
Figure 14-11
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Project operation
An unary operation.
It is applied to one single relation and creates another
relation.
The attributes in the resulting relation are a subset of the
attributes in the original relation.
Figure 14-12
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Join operation
A binary operation.
Combines two relations based on common attributes.
Figure 14-13
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Union operation
A binary operation.
Creates a new relation in which each tuple is either in the
first relation, in the second, or in both.
The two relations must have the same attributes.
Figure 14-14
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Intersection operation
A binary operation.
Creates a new relation in which each tuple is a member in
both relations.
The two relations must have the same attributes.
Figure 14-15
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Difference operation
A binary operation.
Creates a new relation in which each tuple is in the first
relation but not the second.
The two relations must have the same attributes.
14.6
STRUCTURED
QUERY
LANGUAGE
SQL (Structured Query Language)
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Standardized by ANSI and ISO for use on
relational databases.
It is a declarative (not procedural) language,
which means that the users declare what they
want without having to write a step-by-step
procedure.
First implemented by Oracle in 1979.
SQL allows you to combine the following
statements to extract more complex information
from database.
Insert

insert into RELATION-NAME
values ( … , … , … )
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insert into COURSES
values ( “CIS52”,”TCP/IP”, 6 )
Delete

delete from RELATION-NAME
where criteria
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delete from COURSES
where No=“CIS19”
Update
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update RELATION-NAME
set attribute1=value1,
where criteria
update COURSES
set Unit=6
where No=“CIS51”
attribute2=value2, …
Select
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select *
from RELATION-NAME
where criteria
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select *
from COURSES
where Unit=5
Project
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select attribute-list
from RELATION-NAME
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select No, Unit
from COURSES
Join
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select attribute-list
from RELATION1,RELATION2
where criteria
select No,Course-Name,Unit,Professor
from COURSES,TAUGHT-BY
where COURSES.No=TAUGHT-BY.No
Union
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select *
from RELATION1
union
select *
from RELATION2
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select *
from CIS15-Roster
union
select *
from CIS52-Roster
Intersection

select *
from RELATION1
intersection
select *
from RELATION2
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select *
from CIS15-Roster
intersection
select *
from CIS52-Roster
Difference

select *
from RELATION1
minus
select *
from RELATION2
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select *
from CIS15-Roster
minus
select *
from CIS52-Roster
14.7
OTHER
DATABASE
MODELS
Distributed databases
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It is not a new model. It is based on relational model.
The data are stored on several computers that
communicate through the Internet or some private
WAN.
Data are either fragmented, with each fragment
stored at one site, or data are replicated at each site.
 Fragmented
distributed databases
 Replicated distributed databases
Object-Oriented databases
Some application like to see data as a
structure such as a record made of fields.
 Tries to keep the adv. of the relational model
and allows applications to access structured
data.
 In an OODB, objects and their relations are
defined. In addition, each object can have
attributes that can be expressed as fields.
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