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7 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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CS211

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Design Checklist


Planning the Architecture


Client/Server Architecture


Processing Methods


Network Models


Modelling application architecture


System Management and Support


System Design Completion


(Chapter 9)

SYSTEMS design (Phase
-
3) ~ PART 3

-

Application Architecture


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Just as an architect begins a project with
a list of the owner's requirements, a
systems analyst must start with an overall
design checklist.


Before selecting application architecture,
the analyst must consider the following
issues:


Enterprise resource planning


Initial cost and TCO


Scalability


Web integration


Legacy interface requirements


Security


Processing options


DESIGN CHECKLIST


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Every information system involves three
main functions:


Data storage and access methods
.


Application programs

to handle the
processing logic.


An interface

that allows users to
interact with the system.

Depending on the architecture, the three
functions are performed on a server, on
a client, or are divided between the
server and the client.


As you plan the system design, you
must determine where the functions will
be carried out, and the advantages and
disadvantages of each design approach.


PLANNING THE

ARCHITECTURE

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Client/server architecture

generally
refers to systems that divide processing
between one or more networked clients
and a central server.


T
he data file is not transferred from the
server to the client
-

only the request and
the result are transmitted across the
network.

Client/server Architecture

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Table below lists some major differences
between client/server and traditional
mainframe systems.


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Client/Server Design Styles


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Types of Clients

Fat and Thin Client/server designs can be
based on fat or thin clients.


A fat client,

also called a thick client,
design locates all or most of the
application processing logic at the client.


A thin client

design locates all or most
of the processing logic at the server.

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Client/Server Tiers

In a
two
-
tier design
, the user interface
resides on the client, all data resides on
the server, and the application logic can
run either on the server, on the client, or
be divided between the client and the
server.



In a
three
-
tier design
, the user interface
runs on the client and the data is stored
on the server, just as with a two
-
tier
design.



A three
-
tier design also has a
middle
layer

between the client and server that
processes the client requests and
translates them into data access
commands that can be understood and
carried out by the server.


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Middleware

Middleware is software that connects
dissimilar applications and enables them
to communicate and exchange data.



Cost
-
Benefit Issues

To support business requirements,
information systems need to be scalable,
powerful, and flexible. For most
companies, client/server systems offer
the best combination of features to meet
those needs.



Client/Server Performance Issues


What is the answer to enhancing client/
server performance?
Client/server
systems must be designed so the client
contacts the server only when necessary,
and makes as few trips as possible.


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PROCESSING METHODS


ONLINE VS BATCH PROCESSING

An online system handles transactions

when and where they occur and provides

output directly to users.


Online processing systems have four
typical characteristics:


1.
The system processes transactions
completely when and where they
occur.

2.
Users interact directly with the
information system.

3.
Users can access data randomly.

4.
The information system must be
available whenever necessary to
support business functions.


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BATCH PROCESSING

In a batch processing system, data is
collected and processed in groups, or
batches.


Combined Online and Batch
Processing


E
ven an online system can use batch
processing to perform certain routine
tasks.

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When planning a network design, you
must consider
network topology,
protocols, and licensing issues
. You also
must consider
system performance,
security, and interruption issues
.




NETWORK TOPOLOGY


Hierarchical Network:

In a hierarchical
network, one computer (typically a
mainframe) controls the entire network.



Bus Network:

In a bus network, a single
communication path connects the
mainframe computer, server,
workstations, and peripheral devices.

NETWORK MODELS


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Star Network:

A star network has a
central computer with one or more
workstations connected to it that forms a
star.



Ring Network:

A ring network
resembles a circle of computers that
communicate with each other.


NETWORK PROTOCOLS


TCP/IP


NetBIOS


IPX/SPX



LICENSING ISSUES


When considering a network design, it is
important to take into account software
licensing restrictions.

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MODELING APPLICATION

ARCHITECTURE


Multipurpose drawing tools are
available to construct the application
architecture. Example: Microsoft Visio

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SYSTEM MANAGEMENT


AND SUPPORT


PERFORMANCE MANAGEMENT

To monitor system usage, capacity and
trends. Performance management also
can include fine
-
tuning the network
configuration or software settings to
optimise performance.


SYSTEM SECURITY

Maintaining system security involves
two main tasks.



1.
Provisions to assign and monitor
user IDs, passwords, and access
levels.

2.
Handle virus protection and detect
any unauthorised access.


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FAULT MANAGEMENT, BACKUP
AND DISASTER RECOVERY



Fault Management:

Monitoring the
system for signs of trouble, logging all
system failures, diagnosing the problem,
and applying corrective action.



Backup And Disaster Recovery:

Backup
refers to copying data continuously, or at
prescribed intervals. Recovery
procedures involve restoring the data and
restarting the system after an
interruption.



An overall backup and recovery plan
often is called a disaster recovery plan.


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SYSTEMS DESIGN

COMPLETION

The final activities in the systems design
phase are:


Preparing a system design specification,


Obtaining user approval, and


Delivering a presentation to management.


System Design Specification

The system design specification is a
document that presents the complete
design for the new information system
along with
detailed costs, staffing, and
scheduling

for completing the next SDLC
phase
-

systems implementation.



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1.
Management Summary:

Overview of
the project
for company managers and
executives

.


2.
System Components Details:

Includes
the user interface, outputs, inputs,
files, databases, network
specifications.
source documents,
report and screen layouts, DFDs and
0
-
0 diagrams.




3.
Environmental Requirements:

Describes the constraints affecting the
system,
, including any requirements
that involve operations, hardware,
systems software, or security.



A typical system design specification
uses the following structure:

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4.
Implementation Requirements:

Specify start
-
up processing, initial
data entry or acquisition, user
training requirements, and software
test plans.



5.
Time and Cost Estimates:

This
section provides detailed schedules,
cost estimates, and staffing
requirements.


6.
Appendices:

In this section, you
might include copies of documents
from the first three phases if they
would provide easy reference for
readers.


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USER APPROVAL


Users must review and approve the
interface design, report and menu
designs, data entry screens, source
documents, and other areas of the
system that affect them.



Other IT department members also need
to review the system design
specification:



IT management


The programming team


The operations group

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PRESENTATIONS

The presentations give you an
opportunity to explain the system, answer
questions, consider comments' and secure
final approval.


First presentation:

Systems analysts,
programmers, and technical support staff
members



Second presentation:

Department
managers and users from departments
affected by the system
.


Final presentation:

C
ompany
management.