what is System life cycle?

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Answer 1

System Life Cycle
Just like humans, each information system (IS) has a life cycle. An IS is born as an initial concept, is built and used and ultimately is retired when it is no longer useful. The four phases of the Systems Life Cycle (SLC) are Concept and Implementation, Growth, Maintenance, and Decline.
Conceptual and Implementation - In this phase the user identifies information related needs. The requirement for a new (or upgraded system) can be due to environmental pressures (competition, regulation, new technology etc.) or because an older system is no longer providing the required functionality. The user requests the assistance of the systems analyst who studies the problem and offers a solution. During this phase the IS is designed and installed. This phase is fully described in the Waterfall Model section that follows.

Growth - In this phase the IS has been installed and the users are gaining experience with it. They are exploring the system's potential and offering suggestions for upgrade that may be quite substantial. It is during this phase that a post-implementation audit is conducted as a quality assurance measure to ensure that the system does address the needs of the users. During the growth phase usage spreads throughout the organization.

Maintenance - In this phase (which is sometimes named Maturity) the IS is relatively stable. major alterations were primarily conducted in the previous stage. Although the IS may be modified during the maintenance phase the changes typically are slight and the system is considered to be reliable.

Decline - Here the system is becoming outdated and the need for change may become dramatic. Eventually the cost to modernize the IS becomes excessive and a decision is made to replace it. Often a factor that causes decline is the advance of technology that overtakes the potential for a system that was built in the past using technology that is now old and may even be obsolete.

The traditional approach (SLC) to system development is not without problems. Although the SLC has been used successfully for many years it is worth noting some of the issues that the SLC can cause.

Long delivery time - System development time can be quite extensive. This is expecially true of large and complex projects. Not only may the users (clients) become impatient but the needs of the organization may change during the development period and the finished result may not match initial needs.

High expense - Systems are expensive to build. Staff (programmers, analysts, users, etc). must be paid and provided workspace. Time spent by users during system development is usually considered not productive because they are taken away from their regular job responsibilities. A consequence of long development can be opportunity cost to the organization. As resources (people, hardware, etc.) are tied up in the development effort those resources are not available for other organizational needs.

Missed targets - The SLC (and especially the Waterfall Model - see the next section) has been labeled "monolithic." That is because as the development project moves through its various stages it can be difficult to back up to earlier stages to correct problems. As unbelievable as it may seem, sometimes problems that are identified during development are not fixed until after the system is installed and are then corrected as maintenance activities.

High maintenance costs - Maintenance for most information systems costs about 70% of the system's total expenses during its full life cycle. That means that about 30% of cost goes toward analysis, design, implementation, training users and testing the system. How could it be that maintenance costs so much? The answer is that long delivery time coupled with missed targets contribute to systems delivered that do not really meet all user requirements. Fixes to missed requirements can be expensive and during the life of the IS they typically add up to about 70% of total expense.


Waterfall Model
The conceptual and implementation phase of the SLC contains a sequence of stages that are described as the Waterfall Model. Work completed in each stage is passed on and becomes the input basis for work at the next stage. At each point of transfer between stages it is possible that miss-communication may occur and therefore assumptions used for the work in a particular stage may be based on an incorrect understanding. There is little opportunity to back up and correct problems that are propogated this way.

After you study the illustration of the Waterfall Model you will understand why the process can often produce results similar to the childhood game of "telephone." Since different people may be involved at each stage and must communicate with those at the next stage it is understandable how the information passed from stage to stage may become altered as it falls from level to level. If that does happen then the outcome (the completed information system) given the client (the business user) at the end may not quite match the client's expectations as they were expressed in the early stages. Each of the stages are described next.

Problem Identification -In this stage the user and the analyst work together to identify the specific problem to be considered. The user was most likely motivated to call for the help of the system analyst because of experiencing symptoms of a problem. Symptoms might be, for example, customer invoices printing incorrectly or inventory restocking requests not being transmitted to vendors on a timely basis. These are symptoms not problems. In the first case invoices printing incorrectly is a symptom of the larger problem of decreasing customer confidence in the organization.

Feasibililty Study - Once the problem is identified a feasibility study can be conducted to assess whether or not it is possible and practical to solve the problem. The analyst suggests concerns that must be satisifed before a solution can be proposed. Included are considerations of technology (is there technology that can be applied to the problem area), finance (does the organization have the resources to attempt to solve the problem), human resource (will the staff accept a solution to the problem and if not then what will it take to gain the staff's acceptance). The feasibility study is concluded with a report to management which either requests funding to continue the project or recommends project termination due to infeasibility.

Systems Analysis - In this stage the real work of the systems analyst occurs. Given the presumption of the feasibility of creating a solution to the problem the analyst develops a set of alternative solutions. After much analysis and consideration of data the analyst recommends a solution. The details of how the analyst performs this responsibility is described fully elsewhere in this chapter.

System Design - Here the solution proposed by the analyst is developed into a complete technical specification which the programmers and other technical staff will use as a blueprint for their work.

Files, databases, data entry screens and reports are designed. Programming languages and a database management system may be selected. Hardware and other software selections are included in the system design. Programs to be written are identified and each program's logic is completely spelled out. A document which contains all aspects of the system's technical design is prepared as a result of this stage's activity. The design must be approved by all involved before moving to the next stage.

Implementation - Here the system design is made a reality. Programs are written. Hardware and other software is purchased and installed. If necessary, the development staff is trained in the use of new hardware and software so that development can procede. This stage is typically the most time consuming of all in the Waterfall model.

Testing - After the programs are written the system is tested. First individual programs are tested in what is called unit testing. After each program is certified as working properly alone the programs are tested together in what is called a system test. Finally if the programs integrate properly the system is stress tested. Large volumes of real data are processed by the system and an evaluation is made about whether or not the system can handle the load. Any problems that are discovered are either sent back to the programmers to be fixed before moving to the next stage or if considered not critical some problems may be deferred until the maintenance stage.

Conversion The first activity in this stage is training the staff that will use the new information system. Most likely the operation of the system will differ from what they are accustomed to so the amount of training may be extensive. User manuals must be prepared before training begins. For training to be effective it should be provided in special training rooms, away from the normal work site, so that the staff's attention will not be diluted with concerns about other work responsibilities.

After training is complete it is time to "go live" with the new system. There are three common approaches to putting the new system into production:

This can be risky because if the new system fails the organization may have little to fall back on. An advantage of this approach is that it is often the least costly.

Direct Conversion - here the old system is abruptly turned off and the new system turned on.

Phased Conversion - here the old system is gradually turned off and the equivalent parts of the new system gradually turned on. This approach requires the continued use of resources to support both systems but provides a fall back if problems occur with the new system.

Parallel Conversion - here the old and new systems are run at the same time. There is no concern about new system failure because the old system is completely up and running as a fall back. After a period of time (usually one to three months) the old system is shut down as long as the new system has operated properly during this period. This approach is the most costly because resources must be provided to operate both systems and because the staff must enter all business transactions into both systems in parallel. Therefore, the staff must have full knowledge of the operations of both systems and must take the extra time required to operate both systems.

Maintenance - More resources are expended in this stage of a system's life than in any other. Systems are not always delivered as the specifications originally defined. Changes in technology, competition and business practice place demands on an IS that may require upgrading the IS. Typically 70% of a system's lifetime budget is expended in this stage. It has been estimated that a problem identified and fixed during this phase costs 100 times as much as a problem fixed during the analysis phase.

Answer 2

Systems Development Life Cycle (SDLC) is defined by the U.S. Department of Justice (DoJ) as a software development process, although it is also a distinct process independent of software or other Information Technology considerations. It is used by a systems analyst to develop an information system, including requirements, validation, training, and user ownership through investigation, analysis, design, implementation, and maintenance. SDLC is also known as information systems development or application development. An SDLC should result in a high quality system that meets or exceeds customer expectations, within time and cost estimates, works effectively and efficiently in the current and planned information technology infrastructure, and is cheap to maintain and cost-effective to enhance. SDLC is a systematic approach to problem solving and is composed of several phases, each comprised of multiple steps:

* The software concept - identifies and defines a need for the new system
* A requirements analysis - analyzes the information needs of the end users
* The architectural design - creates a blueprint for the design with the necessary specifications for the hardware, software, people and data resources
* Coding and debugging - creates and programs the final system
* System testing - evaluates the system's actual functionality in relation to expected or intended functionality.

The six official phases are:

1. Preliminary Investigation
2. Systems Analysis
3. Systems Design
4. Systems Development
5. Systems Implementation
6. Systems Maintenance

The general phases are:

1. Feasibility Study
2. Analysis
3. Design
4. Implementation
5. Testing
6. Evaluation

Or:

1. Feasibility Study
2. Analysis
3. Design
4. Development
5. Implementation
6. Maintenance

Or:

1. Feasibility Study
2. Analysis
3. Design
4. Implementation
5. Maintenance

Or:

1. Feasibility Study
2. Analysis
3. Design
4. Development
5. Testing
6. Implementation
7. Maintenance

Or:

1. Analysis (Includes Feasibility Study)
2. Design
3. Development
4. Implementation
5. Evaluation

Answer 3

As its name says: Life Cycle:
In simple and brief words it means that all steps/stages/processes needed to do or required to complete to make a working system:
For example : Study / information collection ==> analysis ==> design ==> develop or program ==> debug / test ==> Implement ==> GO live and so on

Answer 4

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