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. 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

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. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

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. 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

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. 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

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 uses flags, 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. 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

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. 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

34. 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

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. 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

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. 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

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. 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

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