Transcript Introduction to Database

Muhammad Emran
Database Systems
Lecture # 3 & 4
Chapter # 2
Database System Concepts and
Architecture
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Elements of the Database
Approach

Enterprise Data Model

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Relational Databases
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Database technology involving tables (relations) representing
entities and primary/foreign keys representing relationships
Use of Internet Technology

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Graphical model showing high-level entities and relationships for
the organization
Networks and telecommunications, distributed databases, clientserver and 3-tier architectures
Database Applications

Application programs used to perform database activities
(create, read, update, and delete) for database users
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One customer may place
many orders, but each
order is placed by a
single customer
 One-to-many
relationship
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One order has many order
lines; each order line is
associated with a single order
 One-to-many relationship
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One product can be in many
order lines, each order line
refers to a single product
 One-to-many relationship
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Therefore, one order involves
many products and one product
is involved in many orders
 Many-to-many relationship
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Relationships established in special columns that provide links between tables
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Database Management System
(DBMS)

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A software system that enables users to
define, create, maintain, and control access to
the database.
(Database) application program: a computer
program (written in any high level language)
that interacts with database by issuing an
appropriate request (SQL statement) to the
DBMS.
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Database Management System
(DBMS)
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Database Approach

Data definition language (DDL).
 Permits
specification of data types, structures and any
data constraints.
 All specifications are stored in the database.

Data manipulation language (DML).
 General
enquiry facility (query language) of the data.
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Database Approach
 Controlled
access to database may
include:

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a security system
an integrity system
a concurrency control system
a recovery control system
a user-accessible catalogue
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Views


Allows each user to have his or her own
view of the database.
A view is essentially some subset of the
database.
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Views - Benefits
 Reduce
complexity
 Provide a level of security
 Provide a mechanism to customize the
appearance of the database
 Present a consistent, unchanging picture of
the structure of the database, even if the
underlying database is changed
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Components of DBMS Environment
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Components of DBMS Environment

Hardware
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Software

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Can range from a PC to a network of computers.
DBMS, operating system, network software (if
necessary) and also the application programs.
Data
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Used by the organization and a description of
this data called the schema.
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Components of DBMS Environment

Procedures

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Instructions and rules that should be applied to the
design and use of the database and DBMS.
People

Who uses the database with different views
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Components of Database Management
System (DBMS)
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DBMS Architecture
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DBMS Architecture

The Internal or Physical Level:
 The
collection of files permanently stored on
secondary storage devices.
 And it provides a low-level description of the physical
database, and an interface between the operating
system's file system and the record structures used in
higher levels of abstraction.
 At this level record types and methods of storage are
defined, as well as how stored fields are represented.
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DBMS Architecture

The Conceptual Level:
 It
presents a logical view of the entire database,
which allows you to bring all the data in the database
together and see it in a consistent manner.
 The first stage in the design of a database is to define
the conceptual view, and a DBMS provides a data
definition language DDL for this purpose.
 The data definition language used to create the
conceptual level must not specify any physical
storage considerations that should be handled by the
physical level. It should not provide any storage or
access details, but should define the information
content only.
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DBMS Architecture

The External or View Level:
 It
provides a window on the conceptual view which
allows the user to see only the data of interest to
them.
 The user can be either an application program or an
end user. Any number of external views can be
defined and they can overlap each other.
 The System Administrator and the DBA are special
cases. Because they have responsibilities for the
design and maintenance for the design and
maintenance of the database, they at times need to
be able to see the entire database. The external and
the conceptual view are functionally equivalent for
these two users.
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Roles in the Database Environment
Data Administrator (DA)
 Database Administrator (DBA)
 Database Designers (Logical and
Physical)
 Application Programmers
 End Users (naive and sophisticated)

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History of Database Systems
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First-generation
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Second generation
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Hierarchical and Network
Relational
Third generation
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Object-Relational
Object-Oriented
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DBs Hierarchical 1960s
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The hierarchical data model organizes
data in a tree structure.
There is a hierarchy of parent and child
data segments.
This structure implies that a record can
have repeating information, generally in
the child data segments.
Data in a series of records, which have
a set of field values attached to it. It
collects all the instances of a specific
record together as a record type.
These record types are the equivalent
of tables in the relational model, and
with the individual records being the
equivalent of rows.
To create links between these record
types, the hierarchical model uses
Parent Child Relationships. These are a
1:N mapping between record types.
This is done by using trees,
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DBs Network 1970s
Data were more naturally modeled
with more than one parent per child.
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So, the network model permitted the
modeling of many-to-many
relationships in data
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The basic data modeling construct in
the network model is the set construct.

A set consists of an owner record
type, a set name, and a member record
type. A member record type can have
that role in more than one set
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Advantages of DBMSs
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Control of data redundancy
Data consistency
More information from the same amount of data
Sharing of data
Improved data integrity
Improved security
Enforcement of standards
Economy of scale
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Advantages of DBMSs
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Balance conflicting requirements
Improved data accessibility and responsiveness
Increased productivity
Improved maintenance through data
independence
Increased concurrency
Improved backup and recovery services
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Disadvantages of DBMSs
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Complexity
Size
Cost of DBMS
Additional hardware costs
Cost of conversion
Performance
Higher impact of a failure
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