Lecture 7 System Architecture

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The Design of System
Architecture
System Architecture

System architecture translates the
logical design of an information
system onto a physical structure
includes hardware, software,
network support, processing
methods, and security.
Deployment Environment

Deployment environment definition bridges
analysis and design
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Hardware
System software
Networking
Common deployment environments in
which system will operate
Related design patterns and architectures
for application software
Single-Computer and Multitier
Architecture

Single-computer architecture

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Mainframe-based
Limited by single machine capacity
Clustered and multi-computer architecture

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Group of computers to provide processing and
data storage capacity
Cluster acts as a single system
Multicomputer hardware/OS can be less similar
than clustered
Single-, Clustered, and Multicomputer Architectures
Centralized and Distributed
Architecture

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Distributes system across several
computers and locations
Relies on communication networks
for geographic connectivity
Client/server architecture dominant
model for distributed computing
Application Architecture
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Complex hardware/networks require
more complex software architectures
There are commonly used approaches
(patterns) for application architecture
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Client/server architecture
Three-layer client/server architecture
Web services architecture
Internet and Web-based application
architecture
Client/Server Computing


Information processing is distributed among
several workstations and servers on a network,
with each function being assigned to the
environment that is best suited to perform it.
The client initiates the requests and the server
responds.
Consolidate the virtues of traditional timeshared mainframe and mini-computer
paradigms with the advantages of personal
computers, workstations, and local area
networks
Components of Client/Server
Computing

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Three interrelated components
Client - the front-end
Server - the back-end
Network - the middle ware
Many to many relationship between
clients and servers.
Client/Server Architecture


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Client/server divides programs into two types
Server – manages information system resources
or provides well-defined services for client
Client – communicates with server to request
resources or services
Advantage – deployment flexibility


Location, scalability, maintainability
Disadvantage – complexity

Performance, security, and reliability
Interaction Among Multiple
Clients and a Single Server
Client/Server Architectural
Process

Decompose application into client and
server programs, modules, or objects
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Identify resources or services that can be
centrally managed by independent software
units
Determine which clients and servers will
execute on which computer systems
Describe communication protocols and
networks that connect clients and servers
Three-Layer Client/Server
Architecture

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Layers can reside on one processor or
be distributed to multiple processors
View layer – accepts user input and
formats and displays processing results
Business logic layer – implements rules
and procedures of business processing
Data layer – manages access to stored
data in databases
Three-Layer Architecture
Client/Server Tiers and
Middleware

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Two-tier design: client - server
Three-tier design:
client – application server – data server
Middleware

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Special utility software that enables the tiers to
communicate and pass data back and forth.
A transparent interface that enables system
designers to integrate dissimilar software and
hardware.
Three-tier Client/Server
System
Client/Server Advantages

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Provide scalability, portability, and
interoperability through standard-based
openness
Respond to the organization’s need for easy
information access, flexibility, smooth
administration, reliability, security and
proficient application development
Mix, match, and combine diverse data
elements located in different, often
incompatible systems
Client/Server Disadvantages

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Acceleration of complexity
High hidden costs
Technical support cost
End-user operations cost
Administration cost
Web Services Architecture

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A client/server architecture
Packages software functionality into
server processes (“services”)
Makes services available to applications
via Web protocols
Web services are available to internal and
external applications

Developers can assemble an application using
existing Web services
Web Services Architecture
WSDL: Web Service Description Language
UDDI: Universal Description, Discovery and Integration
SOAP: 'Simple Object Access Protocol
XML: Extensible Markup Language
Internet and Web-Based
Application Architecture

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Web is complex example of
client/server architecture
Can use Web protocols and browsers
as application interfaces
Benefits

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Accessibility
Low-cost communication
Widely implemented standards
Multi-tiered Web Service
System
Negative Aspects of
Internet Application Delivery
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Breaches of security
Fluctuating reliability of network
throughput
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Throughput can be limited
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Volatile, changing standards
The Design of Communication
Networks
Networks
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Network - A set of interconnected
devices that share a directory and can
thus access each other
The directory provides an address for
each component of the network
If the device is not included in the
directory, it is not part of the network
Components of a Network
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Terminals and workstations
Transmission links
Transmission methods
Nodes and switches
Network architecture and standards
The layered protocol system
concept
send a
letter
mail
sorting
mail
packaging
Application
Application
logical
link
Network
Data link
Physical
physical
link
transportation
receive a
letter
Network
mail
sorting
Data link
mail
unpacking
and checking
Physical
Layered Architecture

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Clear division of functionality gives modular
approach to development and ease of
standardization.
Application independence - software
assumes that services are available - no
need to know about implementation
details.
Facilitates maintenance - can replace/omit
or nominally implement a layer
Classification of Networks
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By technology used: cable,
wireless, …
By topology: ring, bus, star
By geographic scope: LAN, WAN,
MAN
By type of ownership: Public,
Private, VPN
Computer Network

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Set of transmission lines, specialized hardware,
and communication protocols
Enables communication among different users
and computer systems
Local area network (LAN) less than one
kilometer long – connects computers within
single building
Wide area network (WAN) over one kilometer
long – implies much greater, global, distances
Router – directs information within network
A Possible Network
Configuration for RMO
McMaster Campus Networks
The Internet, Intranets, and
Extranets
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Internet – global collection of networks
that use TCP/IP networking protocols
Intranets
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Private networks using same TCP/IP
protocols as the Internet
Limited to internal users
Extranets

Intranets that have been extended outside
the organization
Identify the business criteria for
the telecommunications platform

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Translate business to technology along three
dimensions of business functionality
Reach: the locations/people/organizations to
which we must link
Range: the variety of information and
transactions we must be able to share
Responsiveness: the level of service we
guarantees, in terms of speed, reliability, and
security
Reach
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Levels of Reach
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Within a single location
Across a firm’s domestic locations
Across international locations
To customers and supplies with the same
technology base as the firm’s
To all customers and suppliers
To anyone, anywhere
Connection is not communication
Range
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Range involves the information and
transactions that must be shared across
business functions and processes
Levels of Range
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Simple messages
Access to separate data stores
Independent transactions
Cooperative transactions
Object-oriented thinking
Responsiveness
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Refers to the level of service we must guarantee,
in terms of speed, reliability, and security
Levels of responsiveness
Non-immediate response - need not be on-line
Immediate response - on-line during office hours
- airline
On-demand service - 24 hours a day - police
Perfect service - always work with high security defense
Network Design
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Integrate network needs of new system into
existing network infrastructure
Describe processing activity and network
connectivity at each system location
Describe communications protocols and
middleware that connects layers
Ensure that network capacity is sufficient

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Data size per access type and average
Peak number of access per minute or hour
Network Diagram for RMO Customer Support System
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