spiral methodology provides an iterative and progressive approach to defining the requirements and design of your site using prototyping. Once an operational prototype is reached, the development phase of production starts and you proceed using a waterfall approach. The spiral model suggests that a series of four steps be performed before coding begins. The following briefly describes the activities in each pass of the spiral, starting in the center of the spiral.

1. Determine your objectives, your alternatives for meeting your objectives, and any constraints that must be met.

2. Evaluate each alternative and identify its associated risks. Resolve the risks and create a prototype that refl ects the alternative chosen. In the fi rst pass, you create a rough prototype. Each pass through step 2 yields a more robust prototype based on evaluations from previous prototype evaluations.

3. Evaluate the prototype, make suggestions, and identify issues to be resolved. With each pass through the three, more detailed requirements and designs are created based on each prototype.

4. Plan and commit to the next set of four steps based on the output of step 3.

The number of prototypes depends on the site. The width of the spiral represents the cumulative cost of the project. When an operational prototype has been created, the project is completed following the last steps of the waterfall: development of the site, integration into your organization or other systems, and then site launch.

Advantages

When you are about to undertake a large project and there are several unknowns regarding if or how to proceed, the spiral method offers a way to manage your progress while limiting or avoiding risks. In addition to risk management, the spiral model also provides a clear defi nition of what your system should do and look like. The detailed requirements and design documentation that are created as a result of prototyping provide development with clear direction.

Disadvantages

The time it takes to go from a defi ned need to development might be longer than you like. Similar to the waterfall methodology, you spend time planning your system in detail before proceeding to development. Although the progression of prototypes demonstrates progress, the prototype typically isn’t something you can use.

Another disadvantage is its potential cost. Depending on the prototyping approach you use, the cost to prototype a system could be more than the risk associated with diving into development using another method. Spiral typically is not cost-beneficial for small projects. With that said, given the modularity of Drupal, you could create a prototype step by step with minimal investment. In each step, make note of how the prototype approach would need to be modified to meet your requirements.