Assignment 4 (Due: December 19, 2011, before 01:00pm)

Assessment 4
Systems development models

System development model is a concept that is being use to represent the model of a system. It is also a way in organizing a process in the concept of a system and it is commonly uses by the system analyst in representing a blue print for the system that they are going to make. It is very useful for the system analyst and for the client because this will allow them to visualize the system. It is a practical way to have a system development model to insure the quality and effectiveness of the system. It will also minimize the cost and maintenance of the system because if you have a model, you can see the conflict and possible problem during the deployment of the system. If the system has less error, you will have less maintenance and because of that, there will be less cost.

There are different kinds of system development models for the system. The following are the example of system development models that is base on my research and what I have read from the source define below.

 Waterfall model
 Prototyping model
 Spiral model

Waterfall model

Waterfall model is an oldest system model that is being use and the characteristic of it is that when the phase is not yet done, you can’t proceed to another phase. The people commented and criticize this model because it’s quite impractical and unreal. They call it waterfalls because it’s simply like waterfalls and it is flowing downward. There are different phase that is present in the waterfalls system according to contributor melonfire.



• Requirements analysis
• Design
• Implementation
• Testing
• Installation
• Maintenance

Requirements analysis
As I understand with this phase, this will be the phase that the developer especially the analyst will gather data, analyze problem and what will be the body of the system. In every development of the system model, there is a need of data gathering to have bases. This is a critical part of the system because in this phase, you need to know the possible problem and the possible solution. You need to analyze everything and every details of your system because every detail is very important during the development of the system. You need to understand the system and you need to match the system from the customer or client specification. If the system will not match the client system specification and features then this will be useless because it will not function correctly according to its area of deployment. You can minimize the error during the deployment of the system if you can catch the entire possible problem that may occur and if you can do that, you can minimize the cost because there will be a less maintenance and with respect to that, you will have less cost. Don’t worry if you cant see all the problem because in the other phase, you can fixed it but then, this will be a time consuming and has a high cost. High cost and time consuming because sometimes, you can fix it by repeating it all over again especially if the structure of the system.

Design
After the analysis, you need to design what you have analyzed. You can’t go to this phase that if you are unable to finish the analysis phase because you will base your design from the data that you have gather. If you want to have an effective design, you need to gather all the data that is needed in developing the design. The more accurate your data is, the more effective your design will be. This phase also will address the structure and specification of the client. In designing phase, you need to select the hardware and the software parts, the language and the user interface part of the system. You need to understand also the cost of the design base on the budget that is given to you. The good and ideal design will have a good and strong quality with less cost. If you will select the language of the system, I might prefer that you choose the most secure one and the one that is not merely use by other so that only few people will understand it. The complex the structure is, the secure it will be because the complexity will be another key for security. Security is also need to be design to prevent the hackers and the stronger the security will be, the better protection. In designing the system, you need to make the system to be a user friendly because they are the one who will be using the system. The error can be meant by people or not like when the user is not knowledgeable for the system then they can execute an error that can destroy the system even thou they are not meant to do it.

Implementation
In this phase, you need to build what you have design. If you will implement the design, you need to strictly follow all the design when you implement to minimize the error. In the implementation phase, it is commonly build by a team of people. This may compose of debugger, programmer, graphic designer and people with an expertise when it comes to the hardware part of the computer like computer engineer. It is better if you will choose the people which are expert to their field and you may need a project manager to organize the group. The bottom line is you need to match the system from the system architecture. In implementation part, you need to provide a user manual because not all the people know how to use the system and the system must be a user friendly so that the people that will be using the system will have less error. User manual is a guide intended for the user so that they will understand on how to use the system correctly

Testing
It is required that every system must be tested before deploying it. In the testing phase, you will find the error in the system so that you can correct it. The common problem in the testing phase is the semantics part of the system. Mostly, this is the error of the programmer because its all about construction the language. The result is not what you have expected because maybe because of the wrong logical structure. The logical structure is very hard to detect than the syntax error. There are tools that provide correction if you have the syntax error like java but if the error is all about the logical matter, you will have the hard time to find the problem in the system. It is also the stressful part for the debugger and the best debugger is the programmer itself but you need to have another people to debug your system because base on what our instructor from programming 1 said that sometime someone is better to have a debugger beside the programmer because they can easily see you mistake. The debugger is also has a background from the programming language so that he/she can be an effective debugger.

Installation
After a successful testing of the system, you are now ready to deploy the system. The deployment can be in the internet base or land base connection. Installation part for me is the easiest part of the phase because you just need to deploy it but this will be the hardest part for the user because they are the one that will be using the system and they need to familiarize the function and the feature. If the system is user friendly then the user will have no problem from using the system. This analyzation must be included during the designing phase.

Maintenance
This phase has no end phase because maintenance can be sometimes recommending the system to be reconstructed because of the error that has not been predicted during the development. After you install the system, you need to maintain the performance of the system. You need to update the system so that you can meet the incoming specification because that it will always the nature of the system. You need to upgrade it to insure the quality and to coop up to the fast changing environment.

Advantage
The advantage of the waterfall model is it is easy to use and understand. By just reading the phase, you will know the flow of the system and it is also easy to the part of inexperience people like us. Another advantage is that you can’t go to the next phase by not having the previous phase. As I can see the structure, it is very organize and easy to implement and the simple structure is very effective for the simple yet effective system. Low cost if you will develop a simple and flexible design.

Disadvantage
To proceed from one to another phase, you need to finish it and that is an advantage but sometime this architecture can be found at the disadvantage part of the model. If you have the minimum time to spare, if your team is not yet finish in one of the phase of waterfall model, the project will be frozen and this will be a waste of time. The client is unable to see the system until the developer will finish it. This is one of disadvantage because you need to satisfy your client for the system that you are going to develop. Another disadvantage is that this model is suitable only for the simple system and not the complex one. The reason behind this is if you will build a simple system, you can see the problem clearly and you can prevent in the early stage. Unlike if you will build a more complex structure and the error is not clear. It is impractical to use this model if you developing a complex system because if you can’t see the entire major problem before it is too late, you may repeat and go back to the starting phase again. The waterfall model process is not that visible in the blue print. In order to make a complex system, the design must be more detail and the waterfall is not that detail in structure.


Prototyping model

Base on my readings, prototyping is a model that has more accurate product compare to the waterfall model. Because of the characteristic of the model, the user can clearly see the system during the propagation. It is accurate in terms of the client specification because the prototyping allow the system to be reconstructed according to what the client want. In the prototyping, you are going to build a prototype model and starting from the prototype model, the user will evaluate the design and if there is any problem and error, the developer will redesign or edit the prototype to meet the demand of the user. You need to make their demands because they are the one who will be using the system. This model is a less cost model and effective because you will assume the system that there will be no problem and during the user evaluation, this assumption will be corrected. This is a close to the perfection model because you will discover the entire problem. If the problem has been identified then the new program will come in to meet the specification. I can see that this can have an accurate system product and one goal of this model is to allow the user to be more familiarize the system. In order to make the user and adjust the environment of the system, they need to test even if the system is not yet complete and in order to do that, you need to have a prototype. This is more on execution than planning and they are not required for the major planning but they are more on simulation and trial and error to perfect the system. In short, it is almost all about the demonstration of the system before it is being finalize. The prototyping is also for the system with a rapid development and this is for the system that is need to be develop in a short period of time. The type of model with a less cost because of the maintenance and the time that is being spend during the development.

There are phases that you need to follow when you are developing a prototyping model according to the Bulbul Sharma

• Requirement Analysis
• Quick Design
• Prototype Building
• User Evaluation
• Refine prototype
• Engineer the product

Requirement Analysis
This phase is somehow like the requirement analysis from the waterfall model. The deference between the two is that in the waterfall model, it is very specific and it is more detail but the prototyping model, it is not that detail and it is simple and general in nature. In this phase, the analyst is only gathering all the data that is required for the development of the system. The complexity of the system doesn’t matter in this phase and for that, it makes it more flexible in every system that you want to develop.

Quick design
In quick design, you are designing a simple design base from the simple data that you have been discovered. In quick design, you are just picturing out the perfect design to be evaluated and develop. It doesn’t matter if the design is not perfect because the system will be evaluated during the evaluating phase.

Prototype building
In this phase, the programmer is developing a rapid prototype system base from the quick system design from the previous phase. The prototype model is for the client to familiarize and criticize into the next phase. The prototype building is better compare to the well develop and almost perfect system because if the almost perfect system will not meet the client specification, you need to re edit the design or worst, you will re create it and compare to the prototype building, it is easy to re construct because it is simple and if the client will not like it, its not that costly.

User evaluation
In this phase, the user will have an evaluation and testing. They will give their comment about the system and if there is a further problem them this will be recorded and enhance during in the next phase of the model. The evaluation is a critical part of the system because this will define the client specification. You need to make them satisfy for what they want. In short, you need to meet their specification. This is also a way to see the problem that may encounter during the deployment. It is very practical to have this user evaluation compare to the waterfall model that they predict the problem and then build. In this method, it is more accurate because it is being tested in the real time that just having analyzing and predicting it to happened like the waterfall model.

Refine prototype
In the refine prototype, the system will be enhance and corrected base on the comment and evaluation of the client. The opinion of the client is also important like the security of the system. The goal of this model is to create a prototype, enhance evaluate and create again. That is why it is being called a rapid development. After refining the prototype, you need to consult it again to the client and user to be evaluated further until they will be satisfied and meet the required specification of the system.

Engineer the product
In this phase, you are going to implement the real model of the system that is being specified by the client. The error and problem in creating this final model is less because you already know the exact specification of the client because of the prototype model that you have been created. After creating the real system, you need to go back to the user evaluation for the further enhancement. In this case, you will have few enhancements and you don’t need to rebuild the system all over again and that’s one of the advantages of this system.

Advantage
One thing that I like about this system is that you will satisfy the client to the fullest because during the development, the user will able to see the system and test it and if it necessary to modify it, you can demand and for that. This is also a good model because the system error is being minimized because of the prototyping and if you will have the less error, you can minimize the cost and minimize the maintenance. It is very practical model if you have limited resources yet you need to develop a complex system. It is flexible in any type of system and if you sum up all the cost you spend during the development and further enhancement or upgrade will be less that the costs compare to the waterfall model.

Disadvantage
One problem that I can see in this system model is that this model is not that secure when we talk about the security system. It is not very well planned and for that, it is not that effective sometimes. Security is always involved when you develop a system especially those system which is very confidential like the banking system.


Spiral Model

The spiral model somehow combination of waterfall and prototyping model but there is an additional function which is the risk assessment. In this model, the whole process is being repeated if the client is not satisfied for the result. That explains the structure of a model because it is being arrange in the spiral form. It’s a quite good but by just watching the model, I think it is costly and the success of the system is undefined and also time consuming. The spiral model has only few steps to follow according to the center for technology in government from the University at Albany.

• Project objective
• Risk
• Engineering and production
• Planning and management

Project objective
This phase is the same as the phase of waterfall model but you need to define your objective and know the possible problem that may encounter during the development. You need to balance all things so that the risk will be minimized and the success of the project will be maximized.

Risk
The problem is being identify and being analyze if it is necessary for the team to have a further develop the system and enhance it. You also need to review the objective of the project and balance all things in the system. For me, there is no perfect system but you can build a balance one. Balancing the positive and negative side of the system is a practical way to cover up the system weakness. In the risk management, you may develop an alternative way to resolve the present problem.

Engineering and production
You need to know the cost of the development before you build it further. In this phase, the cost is matter the most because you need to identify and analyze if there will be a further development that you need to do. If the client will stop the operation then the system can still function but the quality is low and if you pursue the project for further development then you need to have budget.

Planning and management
The client will be finalizing the project if it is enough or not. If she/he still thinks that it must be develop further then you need to go back from the starting process again and repeat each phase. The feedback of the client will matter most because they will define the limitation and specification and they also are the one who will shoulder the cost of the project.

Advantage and disadvantage
This model are using waterfall and prototyping model and for that this will inherit the future of the two. One advantage of this model is that the user can see the system during the development. It is a good quality development model and more flexible compare to the prototyping model and another is that this model has risk management to guide the client and development in controlling and preventing the risk. The disadvantage of this is that the model is somehow complex. It is not a user friendly and only applicable to those who are more experience in designing a system. If you have a small system then you apply this, it is not practical because the time and cost is higher.


Conclusion
There are different types of system development model outside. All models are not perfect and it will always matter for what kind of model you want to use in developing your own system. You just need to understand every model so that you will know what model you need to use in order to meet the goal and build a good model for your client


http://www.techrepublic.com/article/understanding-the-pros-and-cons-of-the-waterfall-model-of-software-development/6118423
http://www.ctg.albany.edu/publications/reports/survey_of_sysdev/survey_of_sysdev.pdf
http://www.scribd.com/doc/15243782/System-Development-Model

Identify and discuss at least 3 systems development models .. discuss each phases

There a lot of system development models in which I chose only three, the waterfall model, the spiral model, and the prototyping model. But let us first define system development. It is a process designing, planning and implementing a new system or software. There can be database involved. In the system development, there is a life cycle that explains deeper the roles and responsibilities. It has life cycle to have a pattern to follow in order to have a uniform structure to follow. There are system development models that are existed now. It helps to organize the process of system development. There are different kinds of different models in system developments in which they have different approach in organizing each processes.

In this discussion, it will tackle the 3 different kinds of system development models. As I have I read different models in system development, I chose the waterfall model, the spiral model, and the prototyping model.

• The Waterfall Model

The waterfall lifecycle is the traditional approach to system development. It is used by most system analysts and project managers. It is the earliest method of structured system development. The waterfall model is widely used today because it is the generic model for system development. The waterfall model has different phases. Each phase must be completed before you can proceed to the next phase.

The different phases of Waterfall model:

• Requirement Analysis

In this phase and as I understand, it is the phase where the gathering of data or information occurs. It is said to be the most crucial stage. It is because in this phase, you will meet the client and ask them some questions relating to the system. There is a possibility that miscommunication occurs and maybe you will misinterpret what the clients said to you. In this phase also, includes the visit of the company that you want to analyze. It is important to make sure the requirements are detailed and accurate because it can easily determine the problem of the system and the needed things to improve. In this phase also, you need to analyze the problem of a certain system of the company based on the data that you gathered. The requirement analysis phase is more on the gathering of data and analyzing part. It is important that in this stage is completed before can proceed to the next one.

• Design

The design phase is related to requirement analysis. The design that made is based upon the data that you collected on the first phase. You cannot proceed in this phase without completing the collection of data phase or the requirement analysis. It is very important that the data you gather is be specific and be precise because the more specific the design for the given problem. In this phase, it will be a back and forth a lot of times with the requirement analysis and the collection of data. The design should of course be based on the analysis, and for the project to be the project will be complete. The data that are gathered in the requirement analysis phase are broken down into logical units, so that the software process becomes easy for implementation. To have an effective design for the project, you need to gather all the data needed by the system to improve the system and solve the problem of the system. In design phase also, you need to select the language to use to implement the system, the hardware needed in the system. Also, third parties software is chose in this phase. Every type of data which will be required for the designing of the software is done here in this phase. What type of database will be required, what type of data should be supported are some of the important aspects that are decided in this phase. The algorithm of the process in which the software needs to be designed is made in this phase. This algorithm is used for the actual coding part in the next phase. To sum it up, this is the phase, where the fundamental work for actual programming and implementation is done.

• Implementation

In the implementation phase, this is where the project starts to build. In this phase, the actual development of the software takes place. This phase is also known as coding and verification phase. Like other phases, you cannot proceed to implementation phase without completing the design phase. The algorithms will be use is based upon the product made on the design phase. In implementing the system takes place and very difficult to implement, there is a chance that you will go back to the design phase and have another design to be simple and yet the client will satisfied his or her standards.

• Test

In this phase, the system will be test before it will be given to the clients. This is where the bugs and all the error will occur. The system testing is done. They are normally a series of tests, which are run to check the performance of the software, the user-friendly of the system, how to use it and also to find if any new bugs were introduced into the system, after the previous bugs were fixed. The waterfall model in testing is start all over again, to make the software bug free, as far as possible. In this phase also, the codes designed by programmers are integrated and it is tested if the software works as the specifications provided, according also to the data gathered and according to the specifications of the clients. The setup of the final software which needs to be installed at the clients system is also designed and tested so that the client does not face any problem during the installation of the software. After the test phase and all the bugs are fixed and will meet the client’s specifications and needs, the system is then handed over to the client.

• Maintenance
This is the last phase of the Waterfall model in which the system is given to the client after checking all the bugs of the system. After the deployment of the system, maintenance of it is needed. The system needs to be maintained because to fix the errors when it was turnover to the clients. This is also the phase where change occurs. If the clients want to change something or add something this is the updates happens. Some system needs to improve due to the fact that it is old and needed to be updated. Some system also, those errors will occur during on the client’s time to use. This time, maintenance is needed. During the maintenance phase, support and debugging is provided for all such problems.

We all know now the phases of the Waterfall model, each phases were discussed. Waterfall model has its advantage and disadvantage. Mainly, the advantage of waterfall model is it is used widely by most people around the world and it is easy to use. Also, waterfall model is linear kind of model and we all know those linear models are the simplest model to be implemented. Based on what I have read, one advantage of waterfall model is that the amount of resources required to implement this model is minimal. One great advantage of the waterfall model is that documentation is produced at every stage of the waterfall model development. This makes the understanding of the product designing procedure simpler. Also, after every major stage of software coding, testing is done to check the correct running of the code. Another advantage of this model is that the phase in this model is done one at a time in which you can focus on one phase.

If we have advantage on waterfall model, we also have disadvantage on it. We can say that it is the most perfect model I read but unfortunately there are some disadvantage on it, one of them is that we cannot go back, if the design phase has gone wrong, things can get very complicated in the implementation phase. In this case, we must start all over again and again to come up with a good system design. Another factor is that it happens when the client is not very clear of what he exactly wants from his or her software. Any changes that he mentions in between may cause a lot of confusion and a lot of time to do it. It is a waste of time. Also, small changes or errors that arise in the completed software or system may cause a lot of problem. It may be the cause of malfunctioning of the system. The greatest disadvantage of the waterfall model is that until the final stage of the system development cycle is complete, a working model of the software does not lie in the hands of the client. Thus, he or she is hardly in a position to mention if what has been designed is exactly what he or she had asked for.

In waterfall model, this is most widely used because of its simplicity and easy to understand. Each phase is done one at a time in order for the system analyst or the project manager can focus one phase at a time. Despite the disadvantage of the waterfall model, its advantages is the reason why it is consider the most widely used by most people
• The Spiral Model
Another model on system development is what we called the Spiral Model. Spiral model was defined by Barry Boehm in his 1988 article on A Spiral Model of Software Development and Enhancement. This model was not the first model to discuss iterative development, but it was the first model to explain why the iteration matters. The Spiral Model is also known as the Spiral lifecycle model. The Spiral Model was designed to include the best features from the Waterfall and Prototyping Models, and introduces a new component, the risk-assessment. It combines two system development models to have a better performance in system development. The term spiral is used to describe the process that is followed as the development of the system. Like to the Prototyping Model, an initial version of the system is developed, and then modified based on input received from the client evaluation and recommendation. Unlike the Prototyping Model, the development of each version of the system is designed using the steps involved in the Waterfall Model, the requirement analysis, design, implementation, test and maintenance phase.
The spiral model consists of four quadrants. In quadrant one, it consists of Determining the objectives, alternatives and constraints in which it establish an understanding of the system or product objectives. It also investigates implementation alternatives. In quadrant two, it is more on evaluating Alternatives, Identify and resolve risks. The reason in this quadrant is that to reduce the risk associated with the development decisions. In quadrant three, or Develop, Verify, Next-Level Product. In this quadrant, developing the system occurs. The basic waterfall approach may be employed in which concept of operations, design, development, integration, and test of the next system or product iteration. If appropriate, incremental development approaches may also be applicable. And in the quadrant four, or also known as planning the next phase. In this phase, because it is spiral, the next phase will be plan. The spiral model also consists of four steps, the project objectives, Risk Assessment, Engineering and Production, and Planning and Management.

• Project objectives

In this steps, designing and analyzing is needed. Objective is determined in this step. Planning is also needed. Like the waterfall model, there is a phase whose job is to determine the problem, analyze it and formulate a solution in it. It is just the same in the project objectives. Identifying the possible obstacles are on this steps and alternative approaches are evaluated.

• Risk Assessment
Risk is related to the amount and quality of available information. The less of collection of data, the higher the risk. This is where it examines the risk based upon the data we collected. It is also evaluating each version of the system to determine whether or not development should continue. Example of this after collecting the data it will come up to the solution to increase a cost in money in a project completion and also the span of time to complete the project. In this case, the risk was identified. The client or the developer may decide that it does not make sense to continue with the project.

• Engineering & Production
In this steps, hardware needed is determined, the database used, and also what language to be used. In this phase also is where the implementation takes part. This is where the developers’ time to work. This is also where coding takes place. Software piece is developed.

• Planning and Management
The client is given an opportunity to analyze the results of the version created in the Engineering and Production step. The client can decide if there is something needed to add in the system.

The spiral model has also its advantages and disadvantages. Its advantage is that it can easily estimates the budget needed in the project, the time consume to finish the project. In this way, work will be more progressive because important issues are discovered earlier. Another advantage is that it is more able to cope with the changes that software development. It can easily cope up what will be the change needed. Developers can get their hands in and start working on a project earlier is one of its advantages. There are also disadvantages of spiral model. One disadvantage is that the risk of not meeting budget or schedule on completing the project. Also highly customized limiting re-usability is one of the disadvantages of spiral model.

• Prototyping Model

Another system development model is the prototyping. It is often difficult to know all of your requirements at the beginning of a project. That is why Prototyping model was developed. The development of the program is not based on strict planning, but it is based on the response of the users. The prototyping system development model is based by creating a prototype of a system and continues to create a prototype after a prototype until a perfect system or software is created. The Prototype Model builds from a simple concept of what a program is. From a little concept, the software is updated and tested in a real time environment. The clients will be able to test the system or software and improve the system as it was created. It is different from other system development models.

There are four types of Prototype Models based on their development planning: the Patch-Up Prototype, Nonoperational Prototype, First of a Series Prototype and Selected Features Prototype.

• Patch Up Prototype

This prototype is having more developers. Each developer will work on a specific part of the program. It is subdivided into its developers. After the developers completed the task and finish their work on part of the program, the program will be integrated with each other resulting in a whole new program. It will be combined all the programs. Since every developer is working on different part of the program, Patch up Prototype is a fast development model. If each developer is highly skilled, there is no need to overlap in a specific function of work. This type of prototype needs a strong project manager who can monitor the development of the program.


• Non-Operational Prototype

A non-operational prototype model is used when only a certain part of the program should be updated. Not the whole program will used but a certain part of it. In order the specific part of the program, the other is used using dummy program. Each developer who is assigned with different stages will have to work with the dummy prototype. This kind of prototype is used when there is a certain problems will occur on a certain part of the program.

• First of a Series Prototype

This type of prototype is also known as beta version. This Prototype Model could be very efficient if properly launched. The beta version of the program is deployed and introduced to the clients for testing not the fully completed program. In this case the objective of this kind of prototype is to have feedbacks, suggestions of the system or software. It is a big help for the developers to know in what area of the program they need to focus or may be improve the system or change something.

• Selected Features Prototype

This kind of prototype is more likely on First of a Series Prototype, in which a beta version of the system or software is deployed or launched. Their difference is that instead of giving the public the full version of the software in beta, only selected features or limited access to some important tools in the program is introduced. This is usually done to test the independent feature of the software.

There are advantages of using Prototyping model. One of it is the client does not need to wait long as in the Linear Model. Another advantage is that it can easily receive feedbacks and suggestion from the clients to improve the system. Another factor is that error and bugs of the programs can be detected ahead of time. There is also disadvantage of using prototyping model. One of it is that the client could believe the prototype as the working version. For most developers create a prototype and stick to it even though it has errors. Since the prototype changes from time to time, it’s very difficult to create a document for this software. There are many things that are removed, changed and added in a single update of the prototype and documenting each of them has been proven difficult. The documentation should be updated if something is changed in the system.

There are many system development models out there; they have different approach in implementing a certain system. It depends on the system analyst or the project manager what to use because it depends on the flexibility of system analyst.

References:
http://www.learn.geekinterview.com/it/sdlc/prototype-model.html
http://www.buzzle.com/articles/waterfall-model-advantages-and-disadvantages.html
http://www.pctechguide.com/development-life-cycle/waterfall-software-life-cycle-model
http://www.buzzle.com/articles/waterfall-model-life-cycle.html
http://www.freetutes.com/systemanalysis/sa2-spiral-model.html

On our fourth assignment, we were told to identify and discussed three different types of systems development models. But before anything else, I would like to discuss first what is Systems Development Life Cycle (SLDC) and how it is related with System Development Models.

On the whole, Systems Development Life Cycle, or SDLC is very important in project management. It is a conceptual model which is used as a guide for preparing to planning until maintaining a project. The Systems Development Life Cycle (SDLC) illustrates the different stages that are involved to make an effective information system development project, starting from the preliminary feasibility through the safeguarding of the completed project.

Usually, an SDLC methodology goes after the following steps:

1. Evaluating the existing or accessible system. Flaws and imperfections are identified. All of these are done by interrogating the users of the system as well as seeking advice from the support personnel.

2. Defining the new and latest system requirements. Particularly, the insufficiency in the existing system should be dealt with precise proposals for progress and enhancement.

3. Designing what the newly proposed system. The different plans are put down with reference to the physical construction, hardware, operating systems, programming, communications, and security issues.

4. Developing the new system. Since it is said to be “new system”, the new components and programs must be attained and installed, or if some components and programs from the previous system can still be used, enhancing is very appropriate in order to make the new system function well. Users of the system must undergo trainings in its use, and all phase of routine must be tested to avoid unnecessary delays of work and malfunctioning of the system. If it is essential, at this stage, modification and correction must be made.

5. The system is put into use. There are many different ways to put the system into use. One of those is phasing in the new system, considering the application or location until the old system is slowly but surely interchanged. But to be more practical and maybe cost effective, in some cases, shutting down the old system and executing the new system at the same time is necessary.

6. Comprehensively evaluation should be done by the time the new system is up and operating for a moment. In order to avoid unnecessary malfunctioning or break down of the system, maintenance must be kept up thoroughly all the time. Furthermore, users of the system should be kept up-to-date pertaining to the most recent adjustments and processes.

What were discussed above are the phases or stages of the Systems Development Life Cycle. Basically, different authors have different approach in identifying the SDLC methodology. But bottom line is, they still have the same perceptions on how the SDLC methodology works.

The next thing I will discuss is about the System Development Models and how these models are related in Systems Development Life Cycle.

The Purpose of Systems Development Models

Primarily, Systems development models are used to illustrate the different phases in Systems Development Life Cycle (SDLC) such as planning, analysis, design, development, implementation and maintenance of information systems. Every phase is intended for a detailed function and motivation. Some have the same aims and allocate various common responsibilities. Essentially, developers make use of some kind of system development model to direct the project’s life cycle to be able to guarantee excellent and quality systems are build up concerning to the needs and wants of the business organization.

Different Types of System Development Models

• SYNCHRONIZE-AND-STABILIZE (SYNC-AND-STABILIZE)
One of the models in the Systems Development Life Cycle is the Synchronize-and-stabilize (sometimes just called sync-and-stabilize). It is an SDLC model in which teams work in parallel on individual application modules, repeatedly coordinating their code with that of other teams, and debugging (stabilizing) code on a regular basis all the way through the development procedure. It is said that the sync-and-stabilize model is more advantageous over the older waterfall, which is rigorously chronological in nature. Because sync-and-stabilize development allows parallelism, changes can be done at any point in the process and for that, it can be flexible, and responding to the market requirement changes is easier.

HISTORY

David Yoffie of Harvard University and Michael Cusumano of MIT were the people who created the Synchronize and Stabilize, also known as sync-and-stabilize approach. Cusumano and Yoffie both studied commonalities between processes Microsoft used in developing Internet Explorer and those Netscape Communications Corp. used in developing Netscape Communicator. As the researchers continue their study, among other similarities, they found out both corporation put together all the project code nightly. They both also brought together all the components and tried to stabilize code before it was released. Their findings gave Cusumano and Yoffie the idea to incorporate the successful common strategies of the two projects into the sync-and-stabilize model.
According to Michael Cusumano and Richard Selby, Microsoft Corporation is using the sync-and-stabilize approach in their project development. It is also said that without Synchronize and Stabilize structured approach in Microsoft’s system development, Microsoft would almost certainly never been able to propose, design, construct, produce and ship the products it offers now and plans to offer in the future.

Synchronize and Stabilize Model versus Sequential Model (Waterfall Model)

In Synchronize and Stabilize Model:
 Product development and testing is done in parallel
 Vision statement and evolving specification
 Features prioritized and built in 3 or 4 milestone subprojects
 Frequent synchronization (daily builds) and intermediate stabilizations (milestone)
 “Fixed” release and ship dates and multiple release cycles
 Customer feedback continuous in the development process
 Product and process design so large teams work like small teams
In Sequential Model:
 Separate done in sequence
 Complete “frozen” specification and detailed design before building the product
 Trying to build all pieces of a product simultaneously
 One late and large integration and system test phase at the projects end
 Aiming for feature and product “perfection” in each project cycle
 Feedback primarily after development as inputs for future projects
 Working primarily as a large group of individuals in a separate functional department

Base on the things mentioned above about the synch-and-stabilize model and sequential model, it is somehow clear that the Synchronize and Stabilize Model is more flexible compared to Sequential Model in System Development Life Cycle. Since synch-and-stabilize approach uses parallelism, more works can be done and it is also a cost-effective scheme compared to sequential approach which uses a chronological method.
The Synchronize and Stabilize team process can be summarized as follows:
 Feature Oriented
 Synchronize (daily build) and Stabilize (fix errors at end of each milestone, such that the required set of features is completely functional)
 Product Managers develop a vision statement and feature list based on customer input
 Program Managers develop an initial functional specification based on the vision statement
 Program Managers create schedules and parallel feature teams of 3-8 developers and testers based on the functional specification
 Team members can work autonomously, thus maintaining some creative freedom on the project, provided their work can be combined successfully into the daily builds
 Teams develop their own playful penalties for breaking the daily build, which forces a certain amount of discipline amongst a team, while at the same time remaining democratic
According to the book “How Microsoft Builds” b y Cusumano and Selby, there are phases which is need to under go in synch-and-stabilize approach.
PLANNING PHASE (3-12 months, depending on size of project)
 Vision Statement – Product and program management use extensive customer input to identify and priority-order product features.

 Specification - Based on vision statement, program management and development group defines feature functionality, architectural issues and components interdependencies.
 Schedule And Feature Team Formation ¬- Based on specification document, program management coordinates schedule and arranges feature teams that each contain approximately 1 program manager, 3 to 8 developers, and 3 to 8 testers(who work in parallel 1:1 with developers.)

DEVELOPMENT PHASE (6-12 months)
Project managers coordinate evolution of specification. Developers design, code, and debug. Testers pair with developers for continuous testing.
 Subproject I: most crucial 1/3 features, milestone release I
 Subproject II: second 1/3 features, milestone release II
 Subproject III: final (least critical) 1/3 features, milestone release III --- code complete

STABILIZATION PHASE (3-8 MONTHS)
Program managers coordinate OEMs and ISVs and monitor customer feedback. Developers perform final debugging and code stabilization.
 Internal Testing - Testers recreate and isolate errors.
 External Testing - Thorough testing of complete product within the company.
 Release Preparation - Thorough testing of complete product outside the company by “beta” sites such as OEMs, ISVs, and end users. Prepare final release of “golden master” disk and documentation for manufacturing.

 THE SPIRAL LIFE CYCLE MODEL

Another Systems Development Life Cycle Model is the Spiral Life Cycle Mode. The spiral model, also known as the spiral lifecycle model, is one the systems development lifecycle (SDLC) model used in the field information technology (IT). It is that the spiral model is a combination of prototyping model and waterfall model. In making of a large, expensive and complicated project, spiral model is usually used.
Generally, the process in the spiral life cycle model can be illustrated as follows:
1. The new system requirements are defined in as much detail as possible. Primarily, this phase requires interrogating a number of users in behalf of all the internal and external users as well as the other features of the existing system.
2. Creating an initial drawing or design for the newly proposed system.
3. A first example of the newly proposed system is built from the initial design. This is generally a scaled-down system, and symbolizes an estimation of the distinctiveness and characteristics of the final product.
4. A second sample is developed by a fourfold procedure:
(1) Evaluate - assessing the first example in terms of its potencies, drawbacks, and threats;
(2) Define - classifying the constraints of the second sample;
(3) Plan and Design - setting up and designing the second sample;
(4) Construct and Test - creating and examining the second example.
5. Fundamentally, the customer has the choice or the option to abort the whole project if it will cause an immense risk. For instance, the development cost is beyond the budget of the customer, miscalculation of the operating cost, or any other factor that could result into dissatisfaction in the final product or output, considering the customer’s judgment. For that, it will lead to some bad and negative feedbacks against the company if it happens that the developers did not meet the customer’s wants and needs that force them to back out.
6. The existing prototype is evaluated in the same manner as was the previous prototype, and, if necessary, another prototype is developed from it according to the fourfold procedure outlined above.
7. Since it is called as the spiral model, the procedures are iterated, from the beginning through the end, until the customer will get satisfied, that the developed sample illustrated the final product desired by the customer.
8. After the processes that the prototype undergone, the final system can now be assembled
9. Thorough evaluation and examination is necessary to the final system. Primarily, regular maintenance should be carried out to prevent comprehensive fiasco as well as to minimize delays and downtime.
• Objectives: functionality, performance, hardware/software interface, serious achievement issue, etc.
• Alternatives: construct, recycle, acquire, delegate, etc.
• Constraints: expenditure, timetable, interface, etc.
• Study alternatives which is relative to objectives and constraints
• Identify risks – it defines the lack of experience, new technology, tight schedules, poor process, etc.
• Resolve risks – it describes the evaluation if money could be lost by continuing system development
The following strengths and weaknesses as well as when do we use spiral model is according to Yogi Berra.
Spiral Model Strengths
• Provides early indication of undefeatable risks, without much cost
• Users see the system early because of rapid prototyping tools
• Critical high-risk functions are developed first
• The design does not have to be perfect
• Users can be closely tied to all lifecycle steps
• Early and frequent feedback from users
• Cumulative costs assessed frequently
Spiral Model Weaknesses
• Time spent for evaluating risks too large for small or low-risk projects. This means that spiral model is very time consuming. For that, delays could probably occur.
• Time spent planning, resetting objectives, doing risk analysis and prototyping may be excessive. This may lead to downtime risk. Also, it will cause to outbound the budget and time given.
• The model is complex. Spiral model is complicated because you cannot go into the next phase unless you perfectly done the previous stage.
• Risk assessment expertise is required. Every now and then, it is very important that the process underlying the Spiral model must always be evaluated in order to avoid malfunctioning of the system.
• Spiral may continue for an indefinite period
• Developers must be reassigned during non-development phase activities
• May be hard to define objective, verifiable milestones that indicate readiness to proceed through the next iteration. Basically, the iteration process of the spiral model may lead to some risks that could cause difficulty in doing the system as required in the objective.
When to use Spiral Model
• When creation of a prototype is appropriate
• When costs and risk evaluation is important
• For medium to high-risk projects
• Long-term project commitment unwise because of potential changes to economic priorities
• Users are unsure of their needs
• Requirements are complex
• New product line
• Significant changes are expected (research and exploration)

The following strengths and weaknesses as well as when do we use Rapid Application Development Model is according to Yogi Berra.

• RAPID APPLICATION DEVELOPMENT MODEL (RAD)
Some of us are familiar with the RAD or the Rapid Application Development, which is an idea that the product can be developed and produced more rapidly and of great and higher quality through
• Gathering requirements using workshops or focus groups. It means that method of gathering information is via joining workshops or any scheme where there is so-called “groups” of people.
• Prototyping and early, reiterative user testing of designs
• The re-use of software components. Recycling or reusing the old components of the previous software or system is part of the RAD model activity.
• A rigidly paced schedule that defers design improvements to the next product version
• Less formality in reviews and other team communication
Further Discussion on Rapid Application Development
• Requirements planning phase (a workshop utilizing structured discussion of business problems)
• User description phase – automated tools capture information from users
• Construction phase – productivity tools, such as code generators, screen generators, etc. inside a time-box. (“Do until done”)
• Cutover phase -- installation of the system, user acceptance testing and user training
Rapid Application Development Model Strengths
• Reduced cycle time and improved productivity with fewer people means lower costs
• Time-box approach mitigates cost and schedule risk
• Customer involved throughout the complete cycle minimizes risk of not achieving customer satisfaction and business needs
• Focus moves from documentation to code (WYSIWYG).
• Uses modeling concepts to capture information about business, data, and processes.
Rapid Application Development Model Weaknesses
• Accelerated development process must give quick responses to the user
• Risk of never achieving closure
• Hard to use with legacy systems
• Requires a system that can be modularized
• Developers and customers must be committed to rapid-fire activities in an abbreviated time frame.
When to use Rapid Application Development Model

Experienced programmers are members of the team
RAD is a fast paced SDLC. Developers will be using different tools in order to achieve the goal of building software fast. Although it does not need much coding because of the given set of tools, only experienced programmers could work on these tools. If anything happens to the software, only experienced developers could dig deep into the problem even though they did not encode the program.
Expediting application development
For whatever reasons, developers are hard pressed to build applications fast. Using sets of tools, different software could be created in no time. The participation of the users will be greater since they will work in double time to check if the software is up with the standards.
Quick solution for a business problem
The tools used in developing software have steps or processes that could cater to any business need. If a business needs an answer to their nagging question of productivity and better reporting, RAD could create the software based on the business need. There are lots of software which already have the functions needed by any businesses.
Objective Oriented and Highly Critical Users
Everything starts and ends with the objective. Users have to use the software to achieve the intended goal faster or easier. Different user interface and workflows are based on the realization of the objective. RAD makes the developers focus more on answering the need before creating something on their own. The set of tools could be used to answer the problem. Even the design of the user interface could be influenced by users.
Rapid Application Development Model Phases
Like most SDLCs, RAD also has a step by step process. But unlike other SDLCs, the process of developing a program under RAD is faster. Relying on sets of tools for software development, RAD will no longer have to force us to dig deeper in our coding techniques where we burn an hour or two just to complete a single command.
There are only three phases in Rapid Application Development:
• Planning of Requirements
• Design Workshop
• Implementation.

1. Planning of Requirements

In this stage, developers meet with the project director or manager to generate definite objectives from the preferred program. Primarily, different strategies for development as well as the tools that will be used for development are also put up in a specific project. For business organizations, this stage is very necessary since the projected answer to business concerns will be laid out for the first time. Everything in this stage is hypothetical but it will be working together with the clients or businesses that need a software to answer their business need.

2. Design Workshop
When the plans have been laid out; it is time to start building on the plans. Using the agreed tools and interfaces, developers will start to create different programs based on the business need wants. RAD needs a lot of reaction as it also requires a lot of software iteration. Since RAD already has the set of tools to produce the program, developers will only need to refine the user interface. As tools make it easier to create the real prototypes, users will be able to work on a sample. Comment and implications are appreciated as this will be the bases on of the supplementary software procedures and instructions. Slowly developers and users can come up with one prototype that is almost ready for public use.

3. Implementation Phase
After further refinement, the software will finally be introduced to the business or to their intended users. Even though it has gone through hundreds or even thousands of testing and critique, the stage wherein the software is implemented in a larger scale is different hence new suggestions and bugs should be expected from different users. Developers have to remember these inputs and use it for the next software update. Developers have to be sure that the software update will be correct so that users will abandon the older version. This will prevent the system from malfunctioning since only one version is used.
The difference of Design Workshop to the Implementation Phase is not only in bugs but in software implementation. In Design Workshop, developers have to start from the bottom to impress the users. In the latter phase, developers will only have to work in software updates to ensure wider user acceptance.

Rapid Application Development or RAD takes the Prototype Model of SDLC further. Instead of using codes, developers use different tools and software development kits and bring them all together to create a software. Developers who are time challenged could use this application development. Businesses will also appreciate this software as it’s aimed to answer specific problems. Users’ feedbacks are important in this development cycle since they will suggest whether the program will fit to their specifications and needs.  




References:
http://searchsoftwarequality.techtarget.com/definition/systems-development-life-cycle
http://searchsoa.techtarget.com/definition/synchronize-and-stabilize
https://docs.google.com/viewer?a=v&q=cache:_lGbnm2X9QIJ:citeseerx.ist.psu.edu/viewdoc/download%3Fdoi%3D10.1.1.92.1577%26rep%3Drep1%26type%3Dpdf+synchronize-and-stabilize+%28sync-and-stabilize%29+model+phase&hl=en&gl=ph&pid=bl&srcid=ADGEESh6i-Vo0G04PnDvWEQ_sUOjv4VrcbUV3-EBfKB66HuNWJmeL0YLIIRA8OHv--fhjlaOvVtE-ZqDxgrAGfxSEmXReQWYwH_B-jhH_IAjVlo_SV1macB9kWLmya3QFALg2abHgXjT&sig=AHIEtbSUqX4s3QLilblAlp1E50s9sDShhg
https://docs.google.com/viewer?a=v&q=cache:siLjXXYW-5gJ:condor.depaul.edu/jpetlick/extra/394/Session2.ppt+the+fountain+model+of+SDLC&hl=en&gl=ph&pid=bl&srcid=ADGEEShCfW0_MLC4wRbczfUxrndHTkbwguF9fZuaUCe0RDyOCWyO2PTmaPhHnZ4jRhZZ75maVO_7gVAD2ex5-QIhrj1683hMefBNkak7FkQJCAwd-i0-_aQfEVEEKP177h4mmkvMMWJ7&sig=AHIEtbR77wACNjJYd3McDO_KsR7LIELc9w
http://www.learn.geekinterview.com/it/sdlc/rapid-application-development.html

In everything we have to make there is a life cycle to me follow or the sequence in making the things to be done. To organize our work we must have to steps to follow. In the world of developing a technology there is a certain technology to be follow. In different aspects of the technology there is a different phases to be done.
In developing a system there is a life cycle to be follow. This is called the System Development Life Cycle or the SDLC. So, what is a SLDC? Base on TechTarget, System Development Life Cycle is a conceptual model that is used in project management. There are methodologies in SDLC that must be followed. So, what are the methodologies involved in SDLC? In general the phases in SDLC are first, investigating or evaluating an existing system, secondly, defining the requirements to improve the system, then proposing a plan in developing the improvement, then developing the system until the system is finish, then deploying the system and replace the old one and lastly is doing maintenance work or evaluating the system.
There are different models in SDLC but let us focus only on three models. These are the Waterfall model the original SDLC method, Spiral model and the Agile Model. They have different cycles in different models. First we will discuss the Waterfall Model then the Spiral lastly the Agile Model.
First, what is a Waterfall Model? Base on the article of Nilesh Parekh in Buzzle. The Waterfall method is a traditional approach in developing a system. The first approach of the waterfall was ‘Process Model’ it is introduced and followed widely by software engineering to guarantee the success of the project. Waterfall has different phases to undergo with. These phases are requirement specification, software design, implementation and testing and maintenance.
Let us know the different phases of the waterfall model to further understand each phases. This is also base on the article of Nilesh Parekh in Buzzle. The first phase is the Requirement Specification. The requirement specification or requirement analysis this phase is all about the requirements in developing a system all the needs on the developing process is in this phase. All the functions and components that the end user want to have in a system will be stated here. This phase is the first thing to do by a developer. He/she will undergo an investigation or analyze the entire possible requirement that the end user want to have in a system. Lastly, the developer will document all his/her findings in this phase to serve as guideline in the next phase in the model.
The next phase is system and software design. Before arriving in the coding phase it should analyze first the guidelines of the requirements to plan the flow in developing it. In this phase the guideline of all the requirements are been studied to make a system design. Designing the flow makes the coding part easier because the desire outcome of the system is been seen or the designing team have an idea on the outcome of the system. System design will tell all the system requirements and hardware that is use for running the system. Specifying the system design serve as the input for the next phase of the model.
The next phase on the model is implementation and unit testing. Upon receiving the documentation in system design the work is been divided in modules or units and the coding of the system is started. The first one to develop in small programs is called units, the units will be integrated I the next phase. After the unit is finish it will undergo in testing this time it is referred as the unit testing. It will test the functionalities in each module or units that are done. The result in the test will tell if the specifications in each unit or module have been met.
The next phase on the model is integration and system testing. As the last phase is done in developing each module or units and test the functionalities of it this phase will be up. In integration phase, the units will be integrated into a complete system. After the integration phase, the system is checked all the modules or units if they coordinate in each other and the system behavior in per specification of it. After the checking the system it is delivers to the end user for deployment.
The last phase on the model is operations and maintenance. This is the never-ending phase in the waterfall model. The problems or error in the system that is not founded in the testing method is needed to be fixed. There are problems that are occurred in time in time usage of the system. Maintaining the system makes the problem to be fixed. If the end user wants to add more features in the system it is not anymore under in this last phase it will become the new project of the developer.
These phases are base also in the article that Nilesh Parekh wrote. By following this phases will help the system developer to manage the requirements in developing a system and it will organize the flow in developing the system. It is important to follow each phases in this model if you intended to use this model because you can’t proceed to the next phase if the current phase is not yet done.
Now the advantages and disadvantages in Waterfall Model. This is base also in the article that Nilesh Parekh wrote. First, let us know the advantages in waterfall model. The advantages on the Waterfall Model are the following:
• It is easy to implement. It is easy to implement because in the eyes of the manager it is easy to understand and it reduce the cost of the project. The flow of the project makes it easy to understand.
• It has a clear compartmentalization. By having a clear compartmentalization it is easy to set a schedule in every task in the duration of the project.
• It has step by step flow. Having a step by step flow of the phases makes the work easier because you can’t proceed to the next phase if you can’t finish the current phase. All the work is well organized. There is no overlapping of task in the whole duration of the project.
• It has documentation and testing. Lastly, every end of the phase it has documentation and testing to undergo with to know if the phases have error. Documentation each phase helps to know the other team what are the findings in the last phase so that their work will have a better direction. By testing the system helps to minimize the error that the end user will noticed in the long run.
Now, we know the advantages of a Waterfall Model. Let us know the weakness or the disadvantage of a Waterfall Model. The disadvantages on the Waterfall Model are the following:
• Not all requirements gather as one. There would be circumstances that the demands and the requirements given by the clients are inadequate and they would later demand those needs as you go along with the system. Sometimes the clients will add some requirements in the middle of the development process. This will cause the success of the project in a negatively aspects.
• Problems in each phase are not solved. Not all the problems in phase will be solve in the entire duration of the phase. Not all the problems will be seen in the current phase because there are sometimes cases that the problem will be seen when the other units or modules is develop. It will give a system badly structure.
• The system becomes useless. Lastly, some customers will tell their needs in the progress of the system having a list of their wants makes the system become more useless because of their new demands. The new demands will be meet in the newer version of the system it will cost more to the customer.
Having some of the disadvantages mentioned above the waterfall is one of the widely use model of software engineers. This is the best and easy way to use in developing a system throughout the duration of the project.

This is an example of a Waterfall Model. It shows the flow of the project throughout the entire time of developing it.
There is some models that some developers using it. The next model that will be discussed is the Spiral Model. So let us answer this question, what is a Spiral Model? Base on a PDF file of accaglobal. Having a problem in forward momentum of a Waterfall Model, Boehm developed a model to overcome this problem. Spiral Model is more like a procedure than a life cycle. Spiral Model introduces the activities that are concerned in the process rather than the product. There are two features in Spiral Model the risk analysis and the evolutionary nature of process. The evolutionary development is prioritizing the requirements of the project. After an initial analysis it will identify the features with the highest priority for the initial iteration. After completing each iterations, the user would give feedback on the modified part of the system and that would become the priority in the next feature of the system. This will help the development team to make modification and add more detail to the iteration. In feedback and modification makes the spiral model apart from a purely incremental approach.
The Spiral Model is composed of four quadrants. These quadrants serve as the phases that will be undergo in the project. So, what are these four quadrants stands for? The first quadrant is all about determining the objectives, alternatives and constraints. The second quadrant is all about evaluating the alternatives, identifying and resolving the risk. The third quadrant is all about developing, verifying the next-level product. And the last quadrant or the forth quadrant is all about planning the next phase? Now, let us understand what are the functions in each quadrant that spiral model will come across.
Let me discussed first the fist quadrant of the spiral model. In the first quadrant of the model have three activities to be done after moving to the next quadrant. The activities include in the first quadrant are the following:
• Establishing an understanding of the system or product objectives. In this activity the developer will understand the performance of the system and to know the functionality as well. Setting the objectives of the product makes the team more lighten about the goal of the product.
• Investigate implementation alternatives. Having an alternatives solution in every move you will come across makes the procedure more effectively when facing a problem that is suddenly arise. Having an extra plan on taking the product makes it a better outcome. In this activity you will be designing a plan or modifying it.
• Investigate constraints imposed on the alternatives. In this activity it will make the schedule in every task that was imposed in the last activity and this will know the risk that will be arise in undergoing each alternatives made. After this state it will go to the next quadrant.
The next quadrant is all about evaluating the alternatives, identifying and resolving the risk. So, what are the functions of this second quadrant in Spiral Model? In the second quadrant the activities performed is to select an alternative approach that best satisfies the technical, cost, schedule, support and risk constraints. The focus on this quadrant is ob the risk mitigation. Every alternative is investigated and prototyped to reduce the risk associated in the development decision of the project. This quadrant may involve prototyping, simulating, benchmarking, reference checking and more other risk resolution techniques that will satisfy the risk. If the there is critical operation or technical issues or both of them there will be more detailed prototyping to be added before progressing to the next quadrant. After evaluation all of it and it suites the risk with the best satisfactory solution then it will bring us to the next quadrant.
The next quadrant is all about develop, verify and next-level product. In this quadrant it basically use the waterfall model phases the system design, developing, integration and testing. If the critical operation or technical issues is solved in the last activity it is safe to continue in this activity. It is basically the developing process in this quadrant.
The last quadrant or the forth quadrant is all about planning the next phases. This quadrant is one of the characteristic that is common to all the models. This is the need for advanced technical planning and reviews at the critical staging of the project development. Every cycle of the model culminates with a technical review that assess the status, progress and it reviews the plans and identifies the critical operation and technical issues that will be resolved for the next iteration of the spiral.
By explaining the Spiral Model it makes me realize that it is so hard to understand the cycles of the Spiral Model. But it is the best way to use if you want to avoid risk in the project development period because of the alternatives that you can plot on the cycle on it. It is a mix of Waterfall Method in the Spiral Model.

This is the example of the Spiral Model. It has four quadrants and the activities are in a cycle path.
The last model that I will discuss is the Agile Model. What is an Agile Model? Agile Model is developed by the Agile Alliance in the year 2000 base on the PDF of the accaglobal. It is also called Scrum. Agile Model is an adaptive method rather than predictive because you can change the plan if the clients want to change the features. There are six phases in the Agile Model and these are Pre-Project Planning, Project Initiation, Construction Iteration, Release Iterations, Production and Retirement.
Let me discuss one by one the phases of the Agile Model. First the Pre-Project Planning, in this phase you will define the business opportunity. By defining the business opportunity you can able to know the concern of the client and to know what are the needs to fulfill their satisfaction. The other activity in this phase is to identify the viable of the project. By identifying the viable of the project you can able make a plan on how to execute the phases of the project. The last one is assess the feasibility in assessing the feasibility makes you know the possibility outcome in doing the project.
The next phase is Project Inception. In Project Initiation it is the process in building your development team, assessing the project needs, making designs and what type of environment you will use in the project. In this phase it is more like getting ready your team in facing the project. It is packing your team with all the needs in developing the project.
The next phase is Construction Iteration. In this phase the team will develop the project until the project is done. After assessing the design of the project it will undergo in the development phase and testing phase to know the error of the system and to solve it in this phase.
The next phase is the Release Iteration. In this phase this is the last phase in developing the system. It is more in finalizing the system. Making the test for whole the system after that it is ready to deployment. The system will be deployed after all the test runs have made.
The next phase is the Production. In production phase the system is been watch by the developer even though it is already been deploy to the user community. It is more likely maintaining the system. The production stop when the retirement phase is come.
The last phase in the Agile Model is the Retirement. In retirement phase the system is no longer handled by the developer team. It is because the system is been replaced or the system is no longer been used by the user community. And that is the last phase of the Agile Model.
This is based on the article of Scott Ambler in Ambysoft. Agile Model is more likely a Waterfall Model but in my own understanding the system will be cared of by the developer until the system is retired and there is a lot of time in preparing the team and the project. It covers two phases of the model until it started to develop it.
All the Models that I have discussed are more likely common they have the planning stage of the project. The gathering information phase of the project where is the developer gathered all the possible requirements in the project. There is also the developing phase that will develop the system to its completion and testing phase where the system is been test for the error or risk to be encounter in the running of the program. There is also the deployment of the system also where the developer deploy the system to user community and to test it in the user environment. And the last phase that they were common is the maintenance phase where they will maintain the system until the client will no longer have complains in the system.
If I have to decide what is the best model to be followed or to be use when I will make a system. I will prefer the simplest and the easiest way to follow, the Waterfall Model because it is easy to understand and I think all the models stated above is based on the Waterfall Model. It is the most basic models that anyone should follow. Even though it has disadvantages it always safe to use it, it is also nice to have a foundation in simple model before we went to the complex ones.

Source:
http://www.buzzle.com/editorials/1-5-2005-63768.asp
http://www.freetutes.com/systemanalysis/sa2-spiral-model.html
http://searchsoftwarequality.techtarget.com/definition/systems-development-life-cycle
http://www2.accaglobal.com/pdfs/studentaccountant/bakehouse0506.pdf
http://www.ambysoft.com/essays/agileLifecycle.html
http://searchsoftwarequality.techtarget.com/definition/systems-development-life-cycle