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 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

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

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

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

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

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

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

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

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 Click to see Figure 9-5

Local Area Networks and Wide Area 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 Click to see Figure 9-6

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

Local Area Networks and Wide Area 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 Click to see Figure 9-8

Local Area Networks and Wide Area 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 Click to see Figure 9-9

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

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 Click to see Figure 9-11 Click to see Figure 9-12

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

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 Click to see Figure 9-13 Click to see Figure 9-14

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

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

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

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 Click to see Figure 9-15 Click to see Figure 9-16

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 uses flags, and restoration is possible Physical deletion occurs when data is no longer required

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

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

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

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

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 Click to see Figure 9-17a Click to see Figure 9-17b

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

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

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

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 Click to see Figure 9-18

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

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

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

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 Click to see Figure 9-20

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

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

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 Click to see Figure 9-21

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

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

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

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)

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 Click to see Figure 9-22

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

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