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Systems Analysis and Design 8th Edition Chapter 10 System Architecture Introduction • An effective system combines elements into an architecture, or design, that is flexible, cost-effective, technically sound, and able to support the information needs of the business • System architecture translates the logical design of an information system into a physical structure that includes hardware, software, network support, and processing methods 2 System Architecture Checklist • Enterprise Resource Planning (ERP) – The objective of ERP is to establish a company-wide strategy for using IT resources – Supply chain management (SCM) • Faster response, better customer service, and lower costs • Initial Cost and TCO – During the final design stage, you make decisions that will have a major impact on the initial costs and TCO for the new system – You should review all previous cost estimates 3 System Architecture Checklist • Scalability – Scalability, also called extensibility, refers to a system’s ability to expand, change or downsize easily to meet the changing need of a business enterprise – Especially important in implementing systems that are volume-rated, such as transaction processing systems 4 System Architecture Checklist • Web Integration – An information system includes applications – Web-centric architecture – Avoids many of the connectivity and compatibility problems that typically arise – E-marketplaces 5 System Architecture Checklist • Legacy System Interface Requirements – The new system might have to interface with one or more legacy systems – Interfacing a new system with a legacy system involves analysis of data formats and compatibility – The analyst must know if the new application eventually will replace the legacy system 6 System Architecture Checklist • Processing Options – In planning the architecture, designers also must consider how the system will process data - online or in batches – Provision must be made for backup and speedy recovery in the event of system failure 7 System Architecture Checklist • Security Issues – Security threats and defenses are a major concern to a systems analyst – The analyst must consider security issues that relate to system design specifications – Web-based systems introduce additional security concerns 8 Planning the Architecture • Servers – – – – Server Clients Mainframe architecture Server-based processing 9 Planning the Architecture • Clients – As PC technology exploded in the mid-1980s and 1990s, powerful microcomputers quickly appeared on corporate desktops – Users found that they could run their own word processing, spreadsheet, and database applications – Companies linked the stand-alone computers into networks 10 Planning the Architecture • Clients – Stand-Alone Computing – Local and wide area networks – Client-based processing 11 Client/Server Architecture • Overview 12 Client/Server Architecture • Client/Server Design Styles 13 Client/Server Architecture • Fat and Thin Clients 14 Client/Server Architecture • Client/Server Tiers (page 458) – Two-tier design – Three-tier design • Middleware – Enables the tiers to communicate and pass data back and forth – Provides a transparent interface – Can integrate legacy systems and Web-based applications 15 Client/Server Architecture • Cost-Benefit Issues – Client/server systems enable the firm to scale the system in a rapidly changing environment – Client/server computing also allows companies to transfer applications from expensive mainframes to less expensive client platforms – Client/server systems reduce network load and improve response times 16 Client/Server Architecture • Client/Server Performance Issues – In contrast to the centralized system, a client/server design separates applications and data – Distributed database management system (DDBMS) – The system is scalable, so new data sites can be added without reworking the system design – The system is less likely to experience catastrophic failure 17 Internet-Based Architecture • Developing E-Commerce Solutions In-House 18 Internet-Based Architecture • Packaged Solutions and E-commerce Service Providers – Many vendors offer turnkey systems for companies – Another alternative is to use an application service provider (ASP) – Another option is managed hosting – Consider the experience of other companies in the same industry 19 Internet-Based Architecture • Corporate Portals – A corporate portal can provide access for customers, employees, suppliers, and the public • Cloud Computing – Effectively eliminates compatibility issues – Scaling on demand – Requires significantly more bandwidth – Availability – Security 20 Internet-Based Architecture • Web 2.0 – Envisions a second generation of the web that will enable people to collaborate, interact, and share information more dynamically – Wiki – Collective knowledge – Internet operating system, sharing resources 21 Processing Methods • Online Processing – Because it is interactive, online processing avoids delays and allows a constant dialog between the user and the system – Online processing also can be used with fileoriented systems 22 Processing Methods • Batch Processing – The IT operations group can run batch programs on a predetermined schedule, without user involvement, during regular business hours, at night, or on weekends – Require significantly fewer network resources than online systems 23 Processing Methods • Combined Online and Batch Processing 24 Network Models • The OSI Reference Model (page 471) – The OSI model consists of seven conceptual layers – Each layer performs a specific function – Offers a set of design standards • Network Modeling Tools – As you translate the OSI logical model into a physical model of the networked system, you can use software tools, such as Microsoft Visio 25 Network Models • Network Topology – Hierarchical network • it mirrors the actual operational flow in the organization • One disadvantage of a hierarchical network is that if a business adds additional processing levels, the network becomes more complex and expensive to operate and maintain 26 Network Models • Network Topology – Bus network • Devices can be attached or detached from the network at any point without disturbing the rest of the network • Overall performance declines as more users and devices are added • Today, the bus design is much less popular 27 Network Models • Network Topology – Ring network • One disadvantage of a ring network is that if a network device fails (such as a PC or a server), the devices downstream from the failed device cannot communicate with the network • Multistation Access Unit (MAU) – Manages data flow between connected devicesw 28 Network Models • Network Topology – Star network • Disadvantage of the star design is that the entire network is dependent on the switch • However, in most large star networks, backup switches are available immediately in case of hardware failure 29 Network Models • Routers – Routers differ from switches in that they work at OSI level 3 (IP packets) – Can connect to a larger, dissimilar network, such as the Internet (Gateway) – Proxy server • Connects internal LAN clients to Internet 30 Network Models • Network Protocols – The network must use a protocol – A popular network protocol is Transmission Control Protocol/Internet Protocol (TCP/IP) – A familiar example of a TCP/IP protocol is the file transfer protocol (FTP) • Network Licensing Issues – When considering a network design, it is important to take into account software licensing restrictions 31 Wireless Networks • A wireless local area network, or WLAN • Wireless Network Standards – 802.11 – Institute of Electrical and Electronics Engineers (IEEE) – Versions or amendments to improve bandwidth, range and security – Mbps (megabits per second) 32 Wireless Networks • Wireless Network Standards 33 Wireless Networks • Wireless Network Topologies (pgs. 477-478) – Basic Service Set (BSS) – infrastructure mode – Access point – Extended Service Set (ESS) – Roaming – Independence Service Set (ISS) – peer-to-peer mode 34 Wireless Networks • Wireless Trends – Wi-Fi Alliance – Wi-Fi (wireless fidelity) – BlueTooth (close acces, low power) – On addition to 802.11 protocols for LANs, IEEE is working on 802.16 standards (30 mile range) called: – MANs (metropolitan area networks) – WirelessMAN™ - WiMAX 35 Systems Design Completion • System Design Specification – A typical system design specification uses a structure similar to the following: • • • • • • Executive summary System components System environment Implementation requirements Time and cost estimates Appendices 36 Systems Design Completion • 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 – When the system design specification is complete, you distribute the document to a target group of users, IT department personnel, and company management 37 Systems Design Completion • Presentations – The first presentation is to the systems analysts, programmers, and technical support staff members – Your next presentation is to department managers and users from departments affected by the system – The final presentation is for company management – Management might reach one of three decisions: proceed with systems development, perform additional work on the systems design phase, or terminate the project 38