CP 121_2.pptx about time to be implement

CP 121: Introduction
to DatabaseSystems
Lecture 02: Database system development
lifecycle and Database architecture
By
Madam Muro
Pearson Education © 2009

Lecture Objectives
2
 Main components of an information
system.
 Main stages of database system
development lifecycle.
 Database architecture

Software Depression
 Last few decades have seen proliferation of software
applications, many requiring constant maintenance
involving:
 correcting faults,
 implementing new user requirements,
 modifying software to run on new or upgraded
 platforms.
 Effort spent on maintenance began to absorb resources at
an alarming rate.

Software Depression
 As a result, many major software projects were
 late,
 over budget,
 unreliable,
 difficult to maintain,
 performed poorly.
 In late 1960s, led to ‘software crisis’, now refer to as the
‘software depression’.

Software Depression
 Major reasons for failure of software projects includes:
 lack of a complete requirements specification;
 lack of appropriate development methodology;
 poor decomposition of design into manageable
components.
 Structured approach to development was proposed called
Information Systems Lifecycle (ISLC).

Information System
 Resources that enable collection, management, control,
and dissemination of information throughout an
organization.
 Database is fundamental component of IS, and its
development/usage should be viewed from perspective of
the wider requirements of the organization.

Database System Development
Lifecycle
 Database planning
 System definition
 Requirements collection and
analysis
 Database design
 DBMS selection (optional)

Database System Development
Lifecycle
 Application design
 Prototyping (optional)
 Implementation
 Data conversion and loading
 Testing
 Operational maintenance

Stages of the Database System
Development Lifecycle

Main activities associated with each
stage of the database system
development lifecycle

DATABASE CONCEPTS
DATA ABSTRACTION: Data abstraction is a
process of representing the essential features without
including implementation details. Many database-
systems users are not computer trained, developers
hide the complexity from users through several levels
of abstraction, to simplify users’ interactions with the
system

DATABASE CONCEPTS
There are three level of data abstraction.
(1) Internal Level/Physical Level : The physical level
of data abstraction describes “how” the data are
actually stored. This level represents how data are to
be stored in the database to achieve optimal
runtime performance and storage utilization.
-Data compression and encryption techniques
-storage space allocation
-record placement

DATABASE CONCEPTS
(2)Conceptual/Logical Level : The logical level of
the data abstraction describes “what” data are stored
in the database and what relationships exist among
those data. Thus logical level describes the entire
database.
-All entities, attributes, their relationships
-All constraints on the data

DATABASE CONCEPTS
• (3) External Level/View Level: The view level of
data abstraction describes only part of the entire
database. The view level of abstraction simplify their
interaction with the system. The system may provide
many views for the same database. For example one
user may view date in the form (day, month, year)
while another user may view date in the form (Year,
month, day)

DATABASE CONCEPTS
INSTANCES AND SCHEMAS:
 Instances : The collection of information stored in the
database at a particular moment is called an instance of
the database.
 Schemas : The overall design of the database is called the
database schema. That is, the description of a database is
called the database schema which is specified during
database design and is not expected to change frequently.
 The database schema can be partitioned according to the
level of abstraction.

Database concepts
(a) Physical or Internal Schema: The physical schema,
describes the physical storage structure of the database.
It with the following activities :
(1) Storage space allocation for data and storage.
(2) Record descriptions for storage with stored size for
data items.
(3) Record Placement.
(4)Data compression and data encryption techniques.
This schema uses a physical data model and describes the
complete details of data storage and access path for the
database.

Database concepts
(b) The conceptual or logical schema : The
logical schema describes the structure of the
whole database for a community of users.
The conceptual schema describes the entities,
data types, relationships, user operations and
constraints and hides the details of physical
storage structure.

Database concepts
The conceptual level is concerned with the following
activities :
(i) All entities, their attributes and their relationships.
(ii)Constraint on the data.
(iii)Semantic information about the data.
(iv) Security information.
(v) Checks to retain data consistency and integrity.

Database concepts
(c) External Schema:
Each external schema describes the part of the
database that a particular user group is interested in
and hides the rest of the database from that user
group.

THREE-SCHEMA
ARCHITECTURE AND DATA
INDEPENDENCE

Database concepts
DATAINDEPENDENCE
⚫The ability to change the schema at one level of a
database system without having to change the schema at
the next higher level is called “Data Independence”.
There are two types of data independence :
(1) Physical Data Independence: Physical data
Independence is the ability to change the internal
schema without having to change the conceptual
schema. e.g., By creating additional access structure to improve
the performanceof the retrieval orupdate.

Database concepts
(2) Logical Data Independence : The logical Data
Independence is the ability to change the conceptual
schema without having to change application
programs (external schema).
• c.g., We may change the conceptual schema to expand the
database by adding a record types or data items. OR to
reduced the database by removing data item.

Mappings
• In a DBMS based on the three-schema architecture,
each user group refers only to its own external schema.
Hence, the DBMS must transform a request specified on
an external schema into a request against the conceptual
schema, and then into a request on the internal schema
for processing over the stored database.
• If the request is a database retrieval, the data extracted
from the stored database must be reformatted to match
the user's external view. The processes of transforming
requests and results between levels are called
mappings.

Reasons for three level architecture
Each user should be able to access the same data, but
have a different customised view of the data
Users should not have to deal directly with physical
database storage details
The DBA should be able to change the database
storage structures without affecting the users’views
The internal structure of the database should be
unaffected by changes to the physical aspects of storage
The DBA should be able to change the conceptual
structure of the database without affecting all users

Types of the database systems
The DMBS can be classified according to the number of
users and the database site locations.
1. On the basis of the number of users :
• Single-user DBMS
• Multi-user DBMS
2. On the basis of the site location :
• Centralized DBMS
• Distributed DBMS
• Parallel DBMS
• Client/Server DBMS

Single-user DBMS
Single-user database - supports
only one user at a time.
If user A is using the database user B
or C must wait until user A is through.

CP 121_2.pptx about time to be implement

Centralized database systems
 The centralized database system consists of a single processor
together with its associated data storage devices and other
peripherals. It is physically confined to a single location.
 Centralized DBMS: combines everything into single system
including- DBMS software, hardware, application programs and
user interface processing software
 The management of the system and its data are controlled
centrally form anyone or central site.
 A DBMS is centralized if the data is stored at a single computer
site.
 A centralized DBMS can support multiple users, but the
DBMS and the database themselves reside totally at a single
computer site.

Centralized database system
Advantages of Centralized Database System :
 Most of the functions such as update, backup, query,
control access and so on, are easier to accomplish
in a centralized database system.
 The size of the database and the computer on which
it reside need not have any bearing on whether the
database is centrally located.

Centralized database system
Disadvantages
 When the central site computer or database system
goes down, then every users is blocked from using
the system until the system comes back.
 Communication costs from the terminals to the
central site can be expensive.

Distributed database system
 A distributed database is a collection of multiple logically
interrelated database distributed over a Computer Network.
 A distributed database management system is a software system
that manages a distributed database while making the
distribution transparent to the user.
 In distributed database system, data is distributed across
a variety of different databases.
 These are managed by a variety of different DBMS soft wares
running on a variety of different computing machines
supported by a variety of different operating systems.
 These machines are distributed geographically and connected
together by a variety of communication networks.

 In distributed database system, one application can operate
on data that is distributed geographically on different
machines.
 Thus, in distributed database system, the data might be
distributed on different computers in such a waythat data for
one portion is stored in one computer and the data for
another portion is stored in another.
 Each machine can have data and applications of its own.
However, the users on one computer can access to data
stored in several other computers.
 Therefore, each machine willact as a server for some users and
a client for others.

Advantages of Distributed Database
 Distributed database architecture provides greater
efficiency and better performance.
 Asingle database (on server) can be shared across several
distinct client (application) systems.
 As data volumes and transaction rates increase, users can
grow the system incrementally.
 It causes less impact on ongoing operations when adding
new locations.
 Distributed database system provides local autonomy.

Disadvantages of Distributed Database
 Technical problem of connecting dissimilar machine.
 Software cost and complexity.
 Difficulty in data integrity control.
 Processing overhead.
 Communication network failures.
 Recovery from failure is more complex.

Parallel database system
Parallel Database System
Parallel database systems architecture consists of
a multiple CPUs and data storage disks in parallel.
Hence, they improve processing and input/output
speeds.
Parallel database systems are used in the
applications that have to query extremely large
databases or that have to process an extremely large
number of transactions per second.

Several different architectures can be used for parallel
database systems, which are as follows:
 Shared Memory: All the processors share a
common memory.
 Shared data storage disk: All the processors share a
common set of disks. Shared disk systems are
sometimes called clusters.
 Independent Resources :The processors share neither
a common memory nor common disk.
 Hierarchical: This model is a hybrid of the
proceeding three architectures.

Advantages of Parallel Database System
 Parallel database systems are very useful for the applications that
have to query extremely large database or that have to process
an extremely large number of transactions per second.
 This techniques used to speed-up transaction processing on
 data-server systems.
 In a parallel database systems, the through put (that is, the
number of tasks that can be completed in a given time interval)
and the response time (that is, the amount of time it takes to
complete a single task from the time it is submitted) are very
high.

Disadvantages of Parallel Database System
 In a parallel database system, there is a startup cost
associated with initiating a single process and the startup-
time may overshadow the actual processing time, affecting
speedup adversely.
 Since processes executing in a parallel system often access
shared resources, a slowdown may result from interference
of each new process as it competes with existing
processes for commonly held resources, such as shared
data storage disks, system bus and so on.

Client/server database system
 Client/Server architecture of database system has two logical
components namely client and server.
 Clients are generally personal computer or workstations whereas server is large
workstations.
 The applications and tools of DBMS run on one or more client platforms, while the
DBMS software reside on the sever.
 The server computer is called backend and the client's computer is called frontend.
 These server and client computers are connected via a
computer network.
 The applications and tools act as clients of the DBMS, making requests for its
services.

The client/server architecture is a part of the open
systems architecture in which all computing
hardware, operating systems, network protocols and
other software are interconnected as a network and
work in concert to achieve user goals.
It is well suited for online transaction processing and
decision support applications, which tend to generate
a number of relatively short transactions and require
a high degree of concurrency.

Client server database system
 There are two approaches to implement client/server
architecture. the first approach(shown above), the user
interface and application programs are placed on the client
side and the database system on the server side. This
architecture is called two-tier architecture.
 The application programs that reside at the client side
invoke the DBMS at the server side. The application
program interface standards like Open Database
Connectivity (ODBC) and Java Database Connectivity
(JDBC) are used for interaction between client and server.

 Three-tier architecture is primarily used for web-based
applications. It adds intermediate layer known as
application server (or web server) between the client
and the database server.
 The client communicates with the application server,
which in turn communicates with the database server. The
application server stores the business rules (procedures
and constraints) used for accessing data from database
server. It checks the client’s credentials before
forwarding a request to database server. Hence, it
improves database security.

When a client requests for information, the
application server accepts the request, processes it,
and sends corresponding database commands to
database server.
The database server sends the result back to
application server which is converted into GUI
format and presented to the client.

Advantages of Client/Server Database System
 Client/server environment facilitates in more productive
work by the users and making better use of existing data.
 Client/server database system is more flexible as compared
to the centralized system.
 A single database (on server) can be shared across several
distinct client (application) systems.
 Client/server architecture provide a better DBMS performance.
 Client/server system has less expensive platforms to support
applications that had previously been running only on
mainframe computers.

Disadvantages of Client/Server Database System
 Labor or programming cost is high in client/server
environments, particularly in initial phases.
 There is a lack of management tools for
performance monitoring and tuning and security
control, for the DBMS, client and operating systems
and networking environments

CP 121_2.pptx about time to be implement

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