Lifecycling planning

Lifecycling planning

1. Every software development goes through a lifecycle, which consists of all the activities between the time it is in someone's eye and finally takes its last breath on the last customer's machine.

   • Evolutionary prototyping is a lifecycle model in which you develop the sys- tem concept as you move through the project. Usually you begin by devel- oping the most visible aspects of the system.
     • Evolutionary prototyping is especially useful when requirements are chang- ing rapidly,
     • The design-to-schedule lifecycle model is similar to the staged-release lifecycle model in that you plan to develop the product in successive stages. The difference is that you don't necessarily know at the outset that you'll ever make it to the last release.
       • Evolutionary delivery is a lifecycle model that straddles the ground between evolutionary prototyping and staged delivery. You develop a version of your product, show it to your customer, and refine the product based on customer feedback.

2. The waterfall model is the oldest of all lifecycle. A project progresses through an orderly sequence of steps from the initial software concept through system testing.

   • The waterfall model is document driven, which means that the main work products that are carried from phase to phase are documents.
   • The pure waterfall model helps to minimize planning overhead because you can do all the planning up front. It doesn't provide tangible results in the form of software until the end of the lifecycle.
   • It works well when quality requirements dominate cost and schedule requirements.
     • The disadvantages of the pure waterfall model arise from the difficulty of fully specifying requirements at the beginning of the project.
       • Thus, the first major problem with the waterfall model is that it isn't flexible. You have to fully specify the requirements at the beginning of the project, which may be months or years before you have any working software.
         • summary, the venerable pure waterfall model's weaknesses often make it poorly suited for a rapid-development project.

3. The code-and-fix model is a model that is seldom useful, but it is nonetheless common.

   • This code has 2 advantages, fisrt it has no overhead and the second , it requires little expertise.
     • The design-to-tools lifecycle model is a radical approach that historically has been used only within exceptionally time-sensitive environments.
       • The idea behind the design-to-tools model is that you put a capability into your product only if it's directly supported by existing software tools.

4. Spiral:model is a risk-oriented lifecycle model that breaks a software project up into miniprojects. Each miniproject addresses one or more major risks until all the major risks have been addressed.

   • One of the most important advantages of the spiral model is that as costs increase, risks decrease. The more time and money you spend, the less risk you're taking.
   • It provides at least as much management control as the tra- ditional waterfall model.
   • The only disadvantage of the spiral model is that it's complicated. It requires conscientious, attentive, and knowledgeable management.

5. Modified Waterfalls

   • Most of the weaknesses in the pure waterfall model arise not from problems with these activities but from the treatment of these activities as disjoint, sequential phases.
     • Waterfall with risk reduction is another weaknesses, because it requires you to fully define requirements before you begin architectural design,
   • Peter DeGrace describes one of the modifications to the waterfall model as the "sashimi model."
     • The traditional waterfall model allows for minimal overlapping between phases at the end-of-phase review. This model suggests a stronger degree of overlap.

6. The staged-delivery model is another lifecycle model in which you show soft' ware to the customer in successively refined stages.

   • Here you know exactly what you're going to build when you set out to build it.
     • The primary advantage of staged delivery is that it allows you to put useful functionality into the hands of your customers earlier than if you delivered 100 percent of the project at the end of the project.
       • The main disadvantage of staged delivery is that it won't work without careful planning at both the management and technical levels.
         • One alternative that is sometimes overlooked in the excitement surround- ing a new system is the option to buy software off the shelf., the Off-the-shelf software