1.Waterfall Model - Add to Spiral Life Cycle Model This is a recent model that has been proposed by…

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1.Waterfall Model Waterfall approach was first Process Model to be introduced and followed widely in Software Engineering to ensure success of the project. In "The Waterfall" approach, the whole process of software development is divided into separate process phases. The phases in Waterfall model are: Requirement Specifications phase, Software Design, Implementation and Testing & Maintenance. All these phases are cascaded to each other so that second phase is started as and when defined set of goals are achieved for first phase and it is signed off, so the name "Waterfall Model". All the methods and processes undertaken in Waterfall Model are more visible. The stages of "The Waterfall Model" are: Requirement Analysis & Definition: All possible requirements of the system to be developed are captured in this phase. Requirements are set of functionalities and constraints that the end-user (who will be using the system) expects from the system. The requirements are gathered from the end-user by consultation, these requirements are analyzed for their validity and the possibility of incorporating the requirements in the system to be development is also studied. Finally, a Requirement Specification document is created which serves the purpose of guideline for the next phase of the model. System & Software Design: Before a starting for actual coding, it is highly important to understand what we are going to create and what it should look like? The requirement specifications from first phase are studied in this phase and system design is prepared. System Design helps in specifying hardware and system requirements and also helps in defining overall system architecture. The system design specifications serve as input for the next phase of the model. Implementation & Unit Testing: On receiving system design documents, the work is divided in modules/units and actual coding is started. The system is first developed in small programs called units, which are integrated in the next phase. Each unit is developed and tested for its functionality; this is referred to as Unit Testing. Unit testing mainly verifies if the modules/units meet their specifications. Integration & System Testing: As specified above, the system is first divided in units which are developed and tested for their functionalities. These units are integrated into a complete system during Integration phase and tested to check if all modules/units coordinate between each other and the system as a whole behaves as per the specifications. After successfully testing the software, it is delivered to the customer. Operations & Maintenance: This phase of "The Waterfall Model" is virtually never ending phase (Very long). Generally, problems with the system developed (which are not found during the development life cycle) come up after its practical use starts, so the issues related to the system are solved after deployment of the system. Not all the problems come in picture directly but they arise time to time and needs to be solved; hence this process is referred as Maintenance. Advantages and Disadvantages Advantages The advantage of waterfall development is that it allows for departmentalization and managerial control. A schedule can be set with deadlines for each stage of development and a product can proceed through the development process like a car in a carwash, and theoretically, be delivered on time. Development moves from concept, through design, implementation, testing, installation, troubleshooting, and ends up at operation and maintenance. Each phase of development proceeds in strict order, without any overlapping or iterative steps. Disadvantages The disadvantage of waterfall development is that it does not allow for much reflection or revision. Once an application is in the testing stage, it is very difficult to go back and change something that was not well-thought out in the concept stage. Alternatives to the waterfall model include joint application development (JAD), rapid application development (RAD), synch and stabilize, build and fix, and the spiral model. 2.Prototyping Model The Prototyping Model is a systems development method (SDM) in which a prototype (an early approximation of a final system or product) is built, tested, and then reworked as necessary until an acceptable prototype is finally achieved from which the complete system or product can now be developed. This model works best in scenarios where not all of the project requirements are known in detail ahead of time. It is an iterative, trial-and-error process that takes place between the developers and the users. There are several steps in the Prototyping Model: 1. The new system requirements are defined in as much detail as possible. This usually involves interviewing a number of users representing all the departments or aspects of the existing system. 1. A preliminary design is created for the new system. 2. A first prototype of the new system is constructed from the preliminary design. This is usually a scaled-down system, and represents an approximation of the characteristics of the final product. 3. The users thoroughly evaluate the first prototype, noting its strengths and weaknesses, what needs to be added, and what should to be removed. The developer collects and analyzes the remarks from the users. 4. The first prototype is modified, based on the comments supplied by the users, and a second prototype of the new system is constructed. 5. The second prototype is evaluated in the same manner as was the first prototype. 6. The preceding steps are iterated as many times as necessary, until the users are satisfied that the prototype represents the final product desired. 7. The final system is constructed, based on the final prototype. 8. The final system is thoroughly evaluated and tested. Routine maintenance is carried out on a continuing basis to prevent large-scale failures and to minimize downtime. http://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci1000947,00.htmlAdvantages of Prototyping 1.Users are actively involved in the development 2. It provides a better system to users, as users have natural tendency to change their mind in specifying requirements and this method of developing systems supports this user tendency. 3. Since in this methodology a working model of the system is provided, the users get a better understanding of the system being developed. 4. Errors can be detected much earlier as the system is mode side by side. 5. Quicker user feedback is available leading to better solutions. Disadvantages 1. Leads to implementing and then repairing way of building systems. 2. Practically, this methodology may increase the complexity of the system as scope of the system may expand beyond original plans. 3. V-Model The V-model is a software development model which can be presumed to be the extension of the waterfall model. Instead of moving down in a linear way, the process steps are bent upwards after the coding phase, to form the typical V shape. The V-Model demonstrates the relationships between each phase of the development life cycle and its associated phase of testing. Verification Phases 1. Requirements analysis: In this phase, the requirements of the proposed system are collected by analyzing the needs of the user(s). This phase is concerned about establishing what the ideal system has to perform. However, it does not determine how the software will be designed or built. Usually, the users are interviewed and a document called the user requirements document is generated. The user requirements document will typically describe the systems functional, physical, interface, performance, data, security requirements etc as expected by the user. It is one which the business analysts use to communicate their understanding of the system back to the users. The users carefully review this document as this document would serve as the guideline for the system designers in the system design phase. The user acceptance tests are designed in this phase. 2. System Design: System engineers analyze and understand the business of the proposed system by studying the user requirements document. They figure out possibilities and techniques by which the user requirements can be implemented. If any of the requirements are not feasible, the user is informed of the issue. A resolution is found and the user requirement document is edited accordingly. The software specification document which serves as a blueprint for the development phase is generated. This document contains the general system organization, menu structures, data structures etc. It may also hold example business scenarios, sample windows, reports for the better understanding. Other technical documentation like entity diagrams, data dictionary will also be produced in this phase. The documents for system testing is prepared in this phase. 3. Architecture Design: This phase can also be called as high-level design. The baseline in selecting the architecture is that it should realize all which typically consists of the list of modules, brief functionality of each module, their interface relationships, dependencies, database tables, architecture diagrams, technology details etc. The integration testing design is carried out in this phase. 4. Module Design: This phase can also be called as low-level design. The designed system is broken up in to smaller units or modules and each of them is explained so that the programmer can start coding directly. The low level design document or program specifications will contain a detailed functional logic of the module, in pseudocode - database tables, with all elements, including their type and size - all interface details with complete API references- all dependency issues- error message listings- complete input and outputs for a module. The unit test design is developed in this stage. 4.The Spiral Life Cycle Model This is a recent model that has been proposed by Boehm. As the name suggests, the activities in this model can be organized like a spiral. The spiral has many cycles. The radial dimension represents the cumulative cost incurred in accomplishing the steps dome so far and the angular dimension represents the progress made in completing each cycle of the spiral. The structure of the spiral model is shown in the figure given below. Each cycle in the spiral begins with the identification of objectives for that cycle and the different alternatives are possible for achieving the objectives and the imposed constraints. The next step in the spiral life cycle model is to evaluate these different alternatives based on the objectives and constraints. This will also involve identifying uncertainties and risks involved. The next step is to develop strategies that resolve the uncertainties and risks. This step may involve activities such as benchmarking, simulation and prototyping. Next, the software is developed by keeping in mind the risks. Finally the next stage is planned. The next step is determined by remaining risks. For example, its performance or user-interface risks are considered more important than the program development risks. The next step may be evolutionary development that involves developing a more detailed prototype for resolving the risks. On the other hand, if the program development risks dominate and previous prototypes have resolved all the user-interface and performance risks; the next step will follow the basic waterfall approach. The risk driven nature of the spiral model allows it to accommodate any mixture of specification-oriented, prototype-oriented, simulation-oriented or some other approach. An important feature of the model is that each cycle of the spiral is completed by a review, which covers all the products developed during that cycle, including plans for the next cycle. The spiral model works for developed as well as enhancement projects. Spiral Model Description The development spiral consists of four quadrants as shown in the figure above Quadrant 1: Determine objectives, alternatives, and constraints. Quadrant 2: Evaluate alternatives, identify, resolve risks. Quadrant 3: Develop, verify, next-level product. Quadrant 4: Plan next phases. Although the spiral, as depicted, is oriented toward software development, the concept is equally applicable to systems, hardware, and training, for example. To better understand the scope of each spiral development quadrant, lets briefly address each one. Quadrant 1: Determine Objectives, Alternatives, and Constraints Activities performed in this quadrant include: 1. Establish an understanding of the system or product objectivesnamely performance, functionality, and ability to accommodate change. 2. Investigate implementation alternativesnamely design, reuse, procure, and procure/ modify 3. Investigate constraints imposed on the alternativesnamely technology, cost, schedule, support, and risk. Once the system or products objectives, alternatives, and constraints are understood, Quadrant 2 (Evaluate alternatives, identify, and resolve risks) is performed. Quadrant 2: Evaluate Alternatives, Identify, Resolve Risks Engineering activities performed in this quadrant select an alternative approach that best satisfies technical, technology, cost, schedule, support, and risk constraints. The focus here is on risk mitigation. Each alternative is investigated and prototyped to reduce the risk associated with the development decisions. Boehm describes these activities as follows: . . . This may involve prototyping, simulation, benchmarking, reference checking, administering user questionnaires, analytic modeling, or combinations of these and other risk resolution techniques. The outcome of the evaluation determines the next course of action. If critical operational and/or technical issues (COIs/CTIs) such as performance and interoperability (i.e., external and internal) risks remain, more detailed prototyping may need to be added before progressing to the next quadrant. Dr. Boehm notes that if the alternative chosen is operationally useful and robust enough to serve as a low-risk base for future product evolution, the subsequent risk-driven steps would be the evolving series of evolutionary prototypes going toward the right (hand side of the graphic) . . . the option of writing specifications would be addressed but not exercised. This brings us to Quadrant 3. Quadrant 3: Develop, Verify, Next-Level Product If a determination is made that the previous prototyping efforts have resolved the COIs/CTIs, activities to develop, verify, next-level product are performed. As a result, the basic waterfall approach may be employedmeaning concept of operations, design, development, integration, and test of the next system or product iteration. If appropriate, incremental development approaches may also be applicable. Quadrant 4: Plan Next Phases The spiral development model has one characteristic that is common to all modelsthe need for advanced technical planning and multidisciplinary reviews at critical staging or control points. Each cycle of the model culminates with a technical review that assesses the status, progress, maturity, merits, risk, of development efforts to date; resolves critical operational and/or technical issues (COIs/CTIs); and reviews plans and identifies COIs/CTIs to be resolved for the next iteration of the spiral. Subsequent implementations of the spiral may involve lower level spirals that follow the same quadrant paths and decision considerations. 5.Incremental lifecycle model Incremental model is an evolution of waterfall model. The product is designed, implemented, integrated and tested as a series of incremental builds. It is a popular model software evolution used many commercial software companies and system vendor. Incremental software development model may be applicable to projects where: 1.Software Requirements are well defined, but realization may be delayed. 2. The basic software functionality are required early Advantages Advantages 1.Generates working software quickly and early during the software life cycle. 2.More flexible - less costly to change scope and requirements. 3.Easier to test and debug during a smaller iteration. 4.Easier to manage risk because risky pieces are identified and handled during its iteration. Disadvantages 1. Each phase of an iteration is rigid and do not overlap each other. 2. Problems may arise pertaining to system architecture because not all requirements are gathered up front for the entire software life cycle.