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SYSTEMS ANALYSIS & DESIGN

SYSTEMS ANALYSIS & DESIGN. PHASE 3 SYSTEMS DESIGN System Architecture. Chapter 9. System Architecture. Objectives. Define the term system architecture and describe how it relates to the organization and functions of a business system

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SYSTEMS ANALYSIS & DESIGN

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  1. SYSTEMS ANALYSIS & DESIGN PHASE 3 SYSTEMS DESIGN System Architecture

  2. Chapter 9 System Architecture

  3. Objectives • Define the term system architecture and describe how it relates to the organization and functions of a business system • Discuss major processing methods, including batch, online, centralized, and distributed processing • Describe local and wide area networks, and explain various network configurations, including hierarchical, bus, star, and ring

  4. Objectives • Explain the characteristics of distributed systems and client/server architecture • Discuss the major processing functions of data input, validating, updating, sorting, and reporting • Describe standard backup and recovery methods for batch and online processing systems

  5. Objectives • Discuss the differences between traditional systems development and object-oriented development • Define the contents of the system design specification document

  6. Introduction • System architecture refers to the logical and physical design of a system, including hardware, software, data, procedures, and people • System architecture is the last task in the systems design phase of the SDLC • The end product of the systems design phase is the system design specification

  7. Processing Methods • An information system operates in an environment that contains one or more specific platforms • An environment, or platform, consists of a particular combination of hardware, systems software, and processing methods • Most companies have progressed from multiuser or stand-alone environments to a powerful, interconnected operating environment

  8. Click to see Figure 9-1 Click to see Figure 9-2 Processing Methods • Online processing • Interactive • Allows a dialog between the user and the system • Increases productivity

  9. Processing Methods • Batch processing • Data is collected and processed in groups (batches) • Typical method for large amounts of data that are processed periodically, such as paychecks • Batch processing can take place at off-peak times

  10. Click to see Figure 9-3 Click to see Figure 9-4 Processing Methods • Combined online and batch processing • A retail chain is a typical example of online transaction processing and batch processing of accounting data

  11. Click to see Figure 9-5 Processing Methods • Centralized and distributed processing • Trend has been toward distributed data entry and access, rather than centralized operations • Terminology • Centralized processing • Distributed system • Data communication network • Distributed processing • Distributed database management system (DDBMS) • Data processing center • File server design • Client/server architecture

  12. Click to see Figure 9-6 Local Area Networks and WideArea Networks • Networks are classified as local area networks (LANs) or wide area networks (WANs) depending on geographical scope and equipment required • A network allows hardware, software, and data resources to be shared • Topology is the way a network is configured • A protocol is a set of data transmission standards • A popular protocol is TCP/IP • nodes are individual locations on a network

  13. Click to see Figure 9-7 Local Area Networks and WideArea Networks • Hierarchical network • One computer (typically a mainframe) controls the entire network • Satellite processors control lower levels of processors and devices

  14. Click to see Figure 9-8 Local Area Networks and WideArea Networks • Bus network • A single communication path connects all computers and devices • Information is transmitted in either direction • Devices can be attached or detached at any point without affecting the rest of network

  15. Click to see Figure 9-9 Local Area Networks and WideArea Networks • Star network • A central computer has one or more workstations connected to it that form a star • The entire network depends on the central computer

  16. Click to see Figure 9-10 Local Area Networks and WideArea Networks • Ring network • Resembles a circle of computers that communicate with each other • Data flows in only one direction

  17. Click to see Figure 9-11 Click to see Figure 9-12 Client/Server Systems • Divide processing between a central server and one or more clients • A client handles the entire user interface • Data entry • Editing • Data query • Typical transaction • The client submits a request for information from the server • The server responds with the results

  18. Client/Server Systems • History of client/server systems • Early systems did not produce expected savings • Few clear standards existed • Development costs were high • More hardware and software were required • Problems if handling legacy data • Today, with technology advances, client/server systems represent a major trend in information system architecture

  19. Click to see Figure 9-13 Click to see Figure 9-14 Client/Server Systems • Client/server advantages • Client/server systems are scalable, powerful, and flexible • Businesses can size their systems easily to a changing environment • Communication is possible across multiple platforms • Network load is reduced • Response time is improved

  20. TRADEOFF • File server designs and client/server systems: why would a company choose one approach over another? • Issues to consider • Number of users who require simultaneous access • Size and characteristics of data files • Processing requirements and physical characteristics • Design decisions involve balancing all factors • The best solution is one that will effectively support current and future business operations

  21. A KEY QUESTION • R/Way has several options • Continue with a file-based system running on the current file server and three workstations • Implement a relational database running on the existing file server platform • Design a new client/server environment • R/Way should consider cost, data file characteristics, ability to handle legacy data, projected growth, and network load

  22. Processing Functions • All processing functions must be documented • Data input and validating • Updating • Sorting • Reporting

  23. Click to see Figure 9-15 Click to see Figure 9-16 Processing Functions • Data input and validating • In online processing the system handles data entry, data input, and validation as a transaction is entered • With batch processing, data entry and validation are separate functions, and a specific way to handle transaction errors is necessary • Require all transactions before any processing • Use a program to correct the transaction file • Create a suspense file for transaction errors

  24. Processing Functions • Updating • Updating (file maintenance) is the process of adding, changing, or deleting records in a master or table file • An audit file is required • Deletion methods • Logical deletion usesflags, and restoration is possible • Physical deletion occurs when data is no longer required

  25. Processing Functions • Sorting • A major task in file-based systems • Transaction files must be sorted before a batch update takes place • In a database environment, physical sorting is not necessary because the DBMS uses indexes when processing, accessing, and displaying records

  26. Processing Functions • Reporting • A major function of online and batch processing systems • Reports can be designed with report generators and 4GL tools • Most commercial database programs have report generation capability built into the package

  27. Processing Support • Every system will encounter problems • Hardware failures • Systems software errors • User mistakes • Power outages • The objective is to anticipate problems and develop methods to recover from them

  28. Processing Support • Five major support functions • Backup and recovery • File retention • Restart • Start-up processing

  29. Click to see Figure 9-17b Click to see Figure 9-17a Processing Support • Backup and recovery • Different strategies are required for batch and online processing • Batch processing involves restoring the backup master and running the transaction file again • Online recovery strategies include • Log (journal) files that recreate transactions • Multiple high-capacity disks • Streaming tape devices

  30. Processing Support • File retention • The length of time that a file needs to be stored • Determined by combination of legal and processing requirements • Updating cycles are called generations • Grandparent, parent, and child strategy • Legal requirements must be considered

  31. Processing Support • Restart • After a program is interrupted by an error, the first step is to correct the problem and restart the system • A specific restart procedure is required • Common techniques include the use of checkpoints and program status indicators

  32. Processing Support • Start-up processing • Needed when making the transition from the current system to a new system • Create new master files from existing data • Might require special data conversion programs • Start-up processing and file conversion tasks are discussed in Chapter 11, which covers systems implementation

  33. Click to see Figure 9-18 Software Design • Programs required • Identify specific processing functions for each program, and review all process descriptions • Guidelines • Use a separate update program to maintain each master file • Provide a validation program for each update program that does not perform its own validation • Reduce the number of report programs if possible • Identify any programs required to perform special processing

  34. Click to see Figure 9-19 Software Design • Program documentation • In a file-based system, specific program documentation must be assembled • Program identification • Purpose of the program • Processing requirements

  35. Object-Oriented Design • Basic difference in approach • Traditional systems analysis focuses on data flows and procedures • Object-oriented design stresses a bottoms-up approach that focuses on data rather than data flows • SDLC phases may be less clear in an object-oriented approach

  36. Systems Design Completion • System design specification • Presents the complete design for the new system, along with detailed costs, staffing, and scheduling requirements for the next SDLC phase, systems implementation • Programmers rely on the system design specification as they develop the necessary programs and system functions • The contents of the system design specification depend on the company standards and the complexity of the system

  37. Click to see Figure 9-20 Systems Design Completion • System design specification • Management Summary • System Components Details • Program Design • Output Design • Input Design • File and Database Design • Support Processing Design • Environmental Requirements • Implementation Requirements • Time and Cost Estimates • Appendices

  38. Systems Design Completion • Approvals • Review and approval process continues throughout the SDLC • Obtaining design approval from users is especially important • Other approvals are needed from IS department members and management • The system design specific should be distributed well in advance of the presentation

  39. Systems Design Completion • Technical and management presentations • Several presentations usually are made to • Other information systems department staff • Top IS management • Company management • Various decisions are possible including • Proceed with systems development • Perform additional work on system design • Terminate the project

  40. Click to see Figure 9-21 SOFTWEAR, LIMITED • SWL has decided to use True Blue, a consulting firm, to assist in implementing the new ESIP system • True Blue recommends that the ESIP system be designed as a Microsoft Access application • Relational database environment • Client/server capability • SQL command output

  41. SOFTWEAR, LIMITED • System architecture • The development team includes Jane Rossman, Rick Williams, and Becky Evans • Tasks required • Review of ERDs, record designs, processing considerations, backup /recovery procedures, and controls • Design of tables, queries, forms, reports, macros, and code modules • The ESIP system will be a client/server design, with data stored on the payroll server and clients in payroll and human resources

  42. SOFTWEAR, LIMITED • Planning the system • Define all the tasks the new system will perform • List all reports and other required output • ESIP data to be stored on the payroll server • Objects such as forms, queries, and reports to be stored on client workstations • Separating objects from data will provide better security and reduce network loads

  43. SOFTWEAR, LIMITED • Security • Effective security measures are essential to control user access and updates • Passwords • User and workgroup accounts with permission levels • Input from SWL department heads regarding security levels for users • Users will be allowed to create and modify certain forms and reports

  44. SOFTWEAR, LIMITED • Creating the objects • Preparation • Review ERDs and record designs • Verify that the payroll system permits cross-platform access using open database connectivity (ODBC)

  45. Click to see Figure 9-22 SOFTWEAR, LIMITED • Planning the user interface • Objective is a simple, easy-to-use interface • A main form, or switchboard, will display when the ESIP system starts • All ESIP screens will use buttons, menus, and icons • A prototype of the input screens was developed, and user approval obtained

  46. SOFTWEAR, LIMITED • Using Access Basic for procedures and macros • Access Basic is closely related to Visual Basic • Macros can be used to speed up development time • Other procedures will be written in Access Basic • Allows more powerful data manipulation • Customized error messages

  47. SOFTWEAR, LIMITED • Completing the systems design phase • Complete all documentation • Design backup and recovery, file retention, restart and start-up procedures • Develop and distribute a system design specification and complete output, input, file, and program designs • Conduct a management presentation and obtain approval of the ESIP system design

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