System Development Life Cycle

When traditional systems are being developed using conventional System Analyses and Design methodology, a set structure is adhered to. This is broken down into a series of stages or phases that can be cycled through in such a way that any stage can be returned to for the purpose of improvement after the process of evaluation.

Text books that you reference will discuss the phases of thelife cycle approach to system development. The number of components will vary for each text. The important issue is that it is broken down into component parts or phases and these cover the important aspects of the life cycle.

The following is a summary of the phases discussed in chapter 14 of Computers: Tools for an information Age. Capron, H.L.

Phase 1 - Preliminary Investigation

This is a brief study of the problem to see if there is a feasible solution within the constraints and framework provided by the group wishing for a solution to a problem. A rough plan usually is the result of this study.

Define the problem. - Things to consider:

• What is the nature of the problem? Sometimes the problem is not where the client thinks it is.
• Set the scope of the solution. Determine the boundaries of what has to be investigated and solved.
• What are the objectives in solving the problem? Determine what the client believes is possible. What are the needs that are to be addressed?

This brief investigation should result in a report and should propose further action.

Phase 2 - Analysis

The assumption here is that the project is to go ahead based on the preliminary investigation.

The next task is to gather data. This is achieved by investigating the following.

• Written Documents - manual, reports, forms etc currently used by the system.
• Interviews - ask the people who use the current system. Lots of advantages.
• Questionnaires. Used to get information from large groups of people. Provides trends and patterns. Allows for anonymous and non-biased replies.
• Observation - watching what happens in an organisation will allow the analyst to get a real insight on what happens within an organisation.
• Sampling. Collect data about factors such as quantities, costs and time periods.

• Analysis. Previous tasks produce a lot of data and this must be summarized into a form that allows future tasks viable. Data analysis shows how the current system works. Tools such as Data flow diagrams and Decision Tables allow a proper analysis to be affected.

Phase 3 - Design

This is the planning phase and is based on the previous analysys.

Preliminary design. Considers major aspect of the system to be developed. (centralizes, distributed, online, Personal computer, mainframe, Client /server)

Answer the following questions:

• Should the system be developed in house?
• Should the system be purchased using "off the shelf" products?
• Maybe the sytem can be a modified version of an existing product.
• Can the system be developed in-house or does the expertise need to be outsourced?
• Is there a need to create alternate candidates - ie alternate plans in case of original design failure?

Make a presentation to the systems owners:

• Problems
• Benefits
• Analysy/Design so far
• Schedule
• Cost estimate
• Questions

Detail design

A detailed design includes the following:

• Output forms/screens and procedures.
• Input forms/screens and procedures.
• LDFD / System flowcharts.
• File access and format.
• Database Design
• Communication systems
• Security
• Personal / Human factors
• System processing
• Controls and backup

Phase 4 - Development

Once all of the plans have been made, the system must be developed. This involves programming and testing

Scheduling

Various tools such as Gantt charts and other project management tools are used to plan schedule the tasks required to put convert the plan into a real life system. Check out section for Project Management more information.

Programming

The specifications for the system are converted into logic flowcharts and pseudocode. The computer programmers converts this into the code in the language of choice.

Testing

The programmer tests all aspects of the code for the modules that are developed using appropriate test data (unit testing). These models are then tested as a system which ensures that all of the modules will work together (system testing). Once the system is up and running, real life tests must be performed to ensure the system will work under full load. This is known as volume testing.

Phase 5 Implementation

The final phase is where the system is used. This involves the following;

• Training - User manuals, documentation, hands-on instuction, examples of situations.
• Equipment conversion - any existing equipment such as printers, terminals and servers, and any new systems such as networking components and PC's must be modified, tested, installed, purchased and generally prepared to handle the new solution.
• File conversion - this requires manually retyping, scanning, or writing special programs to convert the old data so it will fit the new system. This can involve a great deal of work.
• System conversion - This is when the new system is put in place and the old system no longer used. The main methods are

• Direct conversion - stop using the old system and start using the new - risky!
• Phased conversion - system "eased" in with users only using small parts of the system to begin with, slowly bringing in the new system over a period of time.
• Pilot conversion - the entire system is implemented in one branch or part of the business to begin with.
• Parallel conversion - both systems are used simultaneously for a period of time - expensive and prolonged.

• Auditing - Audit trail to trace output back to the source. All transactions are recorded. Prevent possible security problems and assist auditors.
• Evaluation - This is very important aspect - Does the system do the job it was intended to do? Testing against preset criteria and independent evaluation teams help verify that the system is functioning properly.
• Maintenance - No system is static. This is an ongoing activity that lasts the lifetime of the system.

Conclusion

In all of the phases above, it is essential to do the best job possible. A situation in a later phase that requires going back to, and redoing an earlier phase is far more expensive than doing a thorough job on an earlier phase. However, normal systems development requires constant evaluation and review of earlier phase to ensure a quality finished product.

Prototyping

A prototype is a limited working model of the complete system that is used to evaluate the system early in the design phase and allow the clients to get a better idea of their needs. It is developed very quickly using special tools such as 4GL tools. Although the prototype may have the basic functionality of the proposed system, much of the components that provide robustness and security are not included. Also, many of the input and output systems are developed to a very low level.

Situations which are best suited to prototyping are when: (System Analysys and Design, Capron,H.L.)

• users have trouble stating requirements.
• a communication gap exists between client and analyst.
• system being developed is high risk or high capital investment.
• analyst lack experience in particular application.
• untried or untested system.

Mike Leishman