SYSTEMS ANALYSIS DESIGN PHASE 3 SYSTEMS DESIGN System

SYSTEMS ANALYSIS & DESIGN PHASE 3 SYSTEMS DESIGN System Architecture

Chapter 9 System Architecture SYSTEMS ANALYSIS & DESIGN 3 E PHASE 3 2

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

Objectives PHASE 3 4 à Explain the characteristics of distributed systems and client/server architecture à Discuss the major processing functions of data input, validating, updating, sorting, and reporting à Describe standard backup and recovery methods for batch and online processing systems SYSTEMS ANALYSIS & DESIGN 3 E

Objectives PHASE 3 5 à Discuss the differences between traditional systems development and object-oriented development à Define the contents of the system design specification document SYSTEMS ANALYSIS & DESIGN 3 E

Introduction PHASE 3 6 à System architecture refers to the logical and physical design of a system, including hardware, software, data, procedures, and people à System architecture is the last task in the systems design phase of the SDLC à The end product of the systems design phase is the system design specification SYSTEMS ANALYSIS & DESIGN 3 E

Processing Methods PHASE 3 7 à An information system operates in an environment that contains one or more specific platforms à An environment, or platform, consists of a particular combination of hardware, systems software, and processing methods à Most companies have progressed from multiuser or stand-alone environments to a powerful, interconnected operating environment SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 3 8 Processing Methods à Online processing à Interactive à Allows a dialog between the user and the system à Increases productivity Click to see Figure 9 -1 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -2

Processing Methods PHASE 3 9 à Batch processing à Data is collected and processed in groups (batches) à Typical method for large amounts of data that are processed periodically, such as paychecks à Batch processing can take place at off-peak times SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 3 10 Processing Methods à Combined online and batch processing à A retail chain is a typical example of online transaction processing and batch processing of accounting data Click to see Figure 9 -3 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -4

PHASE 3 11 Processing Methods à Centralized and distributed processing à Trend has been toward distributed data entry and access, rather than centralized operations à Terminology à Centralized processing à Distributed system à Data communication network à Distributed processing à Distributed database management system (DDBMS) à Data processing center à File server design à Client/server architecture SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -5

Local Area Networks and Wide Area Networks PHASE 3 12 à Networks are classified as local area networks (LANs) or wide area networks (WANs) depending on geographical scope and equipment required à A network allows hardware, software, and data resources to be shared à Topology is the way a network is configured à A protocol is a set of data transmission standards à A popular protocol is TCP/IP à nodes are individual locations on a network SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -6

Local Area Networks and Wide Area Networks PHASE 3 13 à Hierarchical network à One computer (typically a mainframe) controls the entire network à Satellite processors control lower levels of processors and devices SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -7

Local Area Networks and Wide Area Networks PHASE 3 14 à Bus network à A single communication path connects all computers and devices à Information is transmitted in either direction à Devices can be attached or detached at any point without affecting the rest of network SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -8

Local Area Networks and Wide Area Networks PHASE 3 15 à Star network à A central computer has one or more workstations connected to it that form a star à The entire network depends on the central computer SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -9

Local Area Networks and Wide Area Networks PHASE 3 16 à Ring network à Resembles a circle of computers that communicate with each other à Data flows in only one direction SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -10

PHASE 3 17 Client/Server Systems à Divide processing between a central server and one or more clients à A client handles the entire user interface à Data entry à Editing à Data query à Typical transaction à The client submits a request for information from the server à The server responds with the results Click to see Figure 9 -11 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -12

Client/Server Systems PHASE 3 18 à History of client/server systems à Early systems did not produce expected savings à Few clear standards existed à Development costs were high à More hardware and software were required à Problems if handling legacy data à Today, with technology advances, client/server systems represent a major trend in information system architecture SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 3 19 Client/Server Systems à Client/server advantages à Client/server systems are scalable, powerful, and flexible à Businesses can size their systems easily to a changing environment à Communication is possible across multiple platforms à Network load is reduced à Response time is improved Click to see Figure 9 -13 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -14

TRADEOFF PHASE 3 20 à File server designs and client/server systems: why would a company choose one approach over another? à Issues to consider à Number of users who require simultaneous access à Size and characteristics of data files à Processing requirements and physical characteristics à Design decisions involve balancing all factors à The best solution is one that will effectively support current and future business operations SYSTEMS ANALYSIS & DESIGN 3 E

A KEY QUESTION PHASE 3 21 à R/Way has several options à Continue with a file-based system running on the current file server and three workstations à Implement a relational database running on the existing file server platform à Design a new client/server environment à R/Way should consider cost, data file characteristics, ability to handle legacy data, projected growth, and network load SYSTEMS ANALYSIS & DESIGN 3 E

Processing Functions PHASE 3 22 à All processing functions must be documented à Data input and validating à Updating à Sorting à Reporting SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 3 23 Processing Functions à Data input and validating à In online processing the system handles data entry, data input, and validation as a transaction is entered à With batch processing, data entry and validation are separate functions, and a specific way to handle transaction errors is necessary à Require all transactions before any processing à Use a program to correct the transaction file à Create a suspense file for transaction errors Click to see Figure 9 -15 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -16

Processing Functions PHASE 3 24 à Updating (file maintenance) is the process of adding, changing, or deleting records in a master or table file à An audit file is required à Deletion methods à Logical deletion uses flags, and restoration is possible à Physical deletion occurs when data is no longer required SYSTEMS ANALYSIS & DESIGN 3 E

Processing Functions PHASE 3 25 à Sorting à A major task in file-based systems à Transaction files must be sorted before a batch update takes place à In a database environment, physical sorting is not necessary because the DBMS uses indexes when processing, accessing, and displaying records SYSTEMS ANALYSIS & DESIGN 3 E

Processing Functions PHASE 3 26 à Reporting à A major function of online and batch processing systems à Reports can be designed with report generators and 4 GL tools à Most commercial database programs have report generation capability built into the package SYSTEMS ANALYSIS & DESIGN 3 E

Processing Support PHASE 3 27 à Every system will encounter problems à Hardware failures à Systems software errors à User mistakes à Power outages à The objective is to anticipate problems and develop methods to recover from them SYSTEMS ANALYSIS & DESIGN 3 E

Processing Support à Five major support functions à Backup and recovery à File retention à Restart à Start-up processing SYSTEMS ANALYSIS & DESIGN 3 E PHASE 3 28

Processing Support PHASE 3 29 à Backup and recovery à Different strategies are required for batch and online processing à Batch processing involves restoring the backup master and running the transaction file again à Online recovery strategies include à Log (journal) files that recreate transactions à Multiple high-capacity disks à Streaming tape devices Click to see Figure 9 -17 a SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -17 b

Processing Support PHASE 3 30 à File retention à The length of time that a file needs to be stored à Determined by combination of legal and processing requirements à Updating cycles are called generations à Grandparent, and child strategy à Legal requirements must be considered SYSTEMS ANALYSIS & DESIGN 3 E

Processing Support PHASE 3 31 à Restart à After a program is interrupted by an error, the first step is to correct the problem and restart the system à A specific restart procedure is required à Common techniques include the use of checkpoints and program status indicators SYSTEMS ANALYSIS & DESIGN 3 E

Processing Support PHASE 3 32 à Start-up processing à Needed when making the transition from the current system to a new system à Create new master files from existing data à Might require special data conversion programs à Start-up processing and file conversion tasks are discussed in Chapter 11, which covers systems implementation SYSTEMS ANALYSIS & DESIGN 3 E

Software Design PHASE 3 33 à Programs required à Identify specific processing functions for each program, and review all process descriptions à Guidelines à Use a separate update program to maintain each master file à Provide a validation program for each update program that does not perform its own validation à Reduce the number of report programs if possible à Identify any programs required to perform special processing SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -18

PHASE 3 34 Software Design à Program documentation à In a file-based system, specific program documentation must be assembled à Program identification à Purpose of the program à Processing requirements SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -19

Object-Oriented Design PHASE 3 35 à Basic difference in approach à Traditional systems analysis focuses on data flows and procedures à Object-oriented design stresses a bottoms-up approach that focuses on data rather than data flows à SDLC phases may be less clear in an objectoriented approach SYSTEMS ANALYSIS & DESIGN 3 E

Systems Design Completion PHASE 3 36 à System design specification à Presents the complete design for the new system, along with detailed costs, staffing, and scheduling requirements for the next SDLC phase, systems implementation à Programmers rely on the system design specification as they develop the necessary programs and system functions à The contents of the system design specification depend on the company standards and the complexity of the system SYSTEMS ANALYSIS & DESIGN 3 E

Systems Design Completion PHASE 3 37 à System design specification à Management Summary à System Components Details à Program Design à Output Design à Input Design à File and Database Design à Support Processing Design à Environmental Requirements à Implementation Requirements à Time and Cost Estimates à Appendices SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -20

Systems Design Completion PHASE 3 38 à Approvals à Review and approval process continues throughout the SDLC à Obtaining design approval from users is especially important à Other approvals are needed from IS department members and management à The system design specific should be distributed well in advance of the presentation SYSTEMS ANALYSIS & DESIGN 3 E

Systems Design Completion PHASE 3 39 à Technical and management presentations à Several presentations usually are made to à Other information systems department staff à Top IS management à Company management à Various decisions are possible including à Proceed with systems development à Perform additional work on system design à Terminate the project SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 3 40 SOFTWEAR, LIMITED à SWL has decided to use True Blue, a consulting firm, to assist in implementing the new ESIP system à True Blue recommends that the ESIP system be designed as a Microsoft Access application à Relational database environment à Client/server capability à SQL command output SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -21

SOFTWEAR, LIMITED PHASE 3 41 à System architecture à The development team includes Jane Rossman, Rick Williams, and Becky Evans à Tasks required à Review of ERDs, record designs, processing considerations, backup /recovery procedures, and controls à Design of tables, queries, forms, reports, macros, and code modules à The ESIP system will be a client/server design, with data stored on the payroll server and clients in payroll and human resources SYSTEMS ANALYSIS & DESIGN 3 E

SOFTWEAR, LIMITED PHASE 3 42 à Planning the system à Define all the tasks the new system will perform à List all reports and other required output à ESIP data to be stored on the payroll server à Objects such as forms, queries, and reports to be stored on client workstations à Separating objects from data will provide better security and reduce network loads SYSTEMS ANALYSIS & DESIGN 3 E

SOFTWEAR, LIMITED PHASE 3 43 à Security à Effective security measures are essential to control user access and updates à Passwords à User and workgroup accounts with permission levels à Input from SWL department heads regarding security levels for users à Users will be allowed to create and modify certain forms and reports SYSTEMS ANALYSIS & DESIGN 3 E

SOFTWEAR, LIMITED PHASE 3 44 à Creating the objects à Preparation à Review ERDs and record designs à Verify that the payroll system permits crossplatform access using open database connectivity (ODBC) SYSTEMS ANALYSIS & DESIGN 3 E

SOFTWEAR, LIMITED PHASE 3 45 à Planning the user interface à Objective is a simple, easy-to-use interface à A main form, or switchboard, will display when the ESIP system starts à All ESIP screens will use buttons, menus, and icons à A prototype of the input screens was developed, and user approval obtained SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 9 -22

SOFTWEAR, LIMITED PHASE 3 46 à Using Access Basic for procedures and macros à Access Basic is closely related to Visual Basic à Macros can be used to speed up development time à Other procedures will be written in Access Basic à Allows more powerful data manipulation à Customized error messages SYSTEMS ANALYSIS & DESIGN 3 E

SOFTWEAR, LIMITED PHASE 3 47 à Completing the systems design phase à Complete all documentation à Design backup and recovery, file retention, restart and start-up procedures à Develop and distribute a system design specification and complete output, input, file, and program designs à Conduct a management presentation and obtain approval of the ESIP system design SYSTEMS ANALYSIS & DESIGN 3 E