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System Architecture Design

Chapter 10Chapter 10

Alan Dennis, Barbara Wixom, and David Tegarden

John Wiley & Sons, Inc.

Slides by Fred NiedermanEdited by Solomon Negash

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Key Definitions

The system architecture design consists of plans for the hardware, software, communications, security , and global support for the new applicationThe designers must decide if processing will occur in the server (server-based), at the personal computer (client-based), or in some combination of these (client-server based).

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Key Definitions

The network model shows major components of the system, where they are located and how they will be connected to one another.The hardware and software specifications describe these components in detail and aid those responsible for purchase and acquisition of these products.

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COMPUTING ARCHITECTURES

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Functions of the Application System

Data storageData access logicApplication logicPresentation logic

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Architectures

Server basedClient basedClient-server based

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Alternative Servers

In server based architectures, the servers do the work and present the resultsMainframeMinicomputerMicrocomputer (personal computer)

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Server-Based Computing

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Alternative Clients

In client based architectures, clients do most of the work (except data storage) and present the resultsTerminalsMicrocomputer (personal computer)Special purpose terminals (ATMs, kiosks, Palm Pilots, and many others)

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Client-Based Computing

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Client-Server-Based Computing (2 Tiers)

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Client-Server Attributes

Typical ProsCompatible with web-based system designScaleableWork with multiple vendors/productsNo central point of failure

Typical Cons/Limits

ComplexityNew programming languages and techniques (stress for personnel)More complex to update

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Client-Server -- Three Tiers

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Client-Server -- Four Tiers

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N-Tiered Client-Server Attributes

Typical ProsSeparates processing to better balance loadMore scaleable

Typical Cons/Limits

Greater load on the networkMore difficult to program and test

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Distributed Objects Computing

Middleware between clients and serversUpdate middleware when changing client codeMay reduce efficiency of the applicationCORBADCOM

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Realities of Infrastructure Design

Most often the infrastructure will be in placeCoordination of infrastructure components is very complexThe application developer will need to coordinate with infrastructure specialists

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Selecting a Computing Architecture

Server-Based Client-based Client-server

Cost of infrastructure Very high Medium Low

Cost of development Medium Low High

Ease of development Low High Low-medium

Interface capabilities Low High High

Control and security High Low Medium

Scalability Low Medium High

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Your Turn

Consider the course registration system at your university:What computing architecture does it use?What computing architecture would you use if you were replacing it today?

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INFRASTUCTURE DESIGN

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The Network Model

No standard formatConveys complexity of the system and how components fit togetherComponents are

ClientsEquipmentConnection to external systems or networks

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Top-Level Network Model

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Hardware and Software Specification

Used if new hardware or software must be purchasedActual acquisition of hardware and software usually left to a purchasing department -- especially in larger firms

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Steps in Hardware and Software Specification

Note hardware in low-level network model to create list of needed hardwareDescribe equipment in as much detail as possibleConsider whether increased processing and traffic will absorb unused hardware capacityNote all software running on each hardware component

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GLOBAL ISSUES

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Global Requirements

Multilingual requirementsConcurrent multilingual systemsDiscrete multilingual systems

Local versus centralized controlUnstated norms (e.g. dates, currency)24-7 SupportCommunications infrastructure

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SECURITY

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Identifying Threats to the System

A threat is any potential adverse occurrence that can do harm to the application or its dataThreats come from internal as well as external sourcesCategories of threats

Disruptions, destruction and disasterUnauthorized access

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Most Common Threats

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Assessing the Risk of Each Threat

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Creating Controls

A control is something that mitigates or stops a threatControls include

redundancyfault tolerant serversdisaster recovery plansanti-virus software

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Additional Controls Include

A security policyPasswords and encryptionFirewalls

What sort of computer architecture would you recommend for your project?Explain your preference.

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SummaryThe three fundamental computing architectures are server-based, client-based, and client-server based.The network model shows technical components of the system and their geographic location throughout the organization.Hardware and software must be specified for acquisition in the projectThe systems analyst needs to also account for global issues and security measures.