The Spiral Method and EVMS

The Spiral method is an iterative approach to developing software used on many contracts. The contract will specify capabilities that are required and include multiple iterations/spirals, each with its own requirements, design, implement and test cycles.

The basic principle of the Spiral approach is to minimize project risk by breaking a project into smaller segments and provide more ease-of-change during the development process, as well as provide the opportunity to evaluate risks and weigh consideration of project continuation throughout the life cycle.

Spirals are not as tight as in the Agile model where daily iterations are the norm. Spirals might be anything from a few months to 2 years.

The Earned Value Management approach fits well with Spiral Development.  EVM includes techniques such as Planning Packages for holding budget for future work that is not yet detailed, and the Rolling Wave concept for breaking out planning packages into more detail as they come into the planning horizon.

In the contracting environment, the customer and contractor agree a number of spirals and a set of capabilities to be targeted for each spiral with a high-level budget allocation and timeframe for each spiral.

Near-term work in the current spiral is planned in detail to the work package/task level.

Future spirals are included with less detail, represented as Planning Packages or Summary Level Planning Packages. As the current spiral nears completion, requirements definition for the next phase commences and the PPs and SLPPs are decomposed to Control Accounts and Work Packages in the EVMS.

When applied correctly the combination of the Spiral model and EVMS provide flexibility to adapt to changing needs, increased understanding with the objective measurement techniques and metrics of EVMS.

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