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

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

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

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

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

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

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

Planning the Architecture Servers Server Clients Mainframe architecture Server-based processing

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

Planning the Architecture Clients Stand-Alone Computing Local and wide area networks Client-based processing

Client/Server Architecture Overview

Client/Server Architecture Client/Server Design Styles

Client/Server Architecture Fat and Thin Clients

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

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

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

Internet-Based Architecture Developing E-Commerce Solutions In-House

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

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

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

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 file-oriented systems

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

Processing Methods Combined Online and Batch Processing

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

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

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

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

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

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

Network Models Network Protocols Network Licensing Issues 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

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)

Wireless Networks Wireless Network Standards

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

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

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

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

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