18.4 Develop and Deploy Incrementally

In theory, the most cost-effective way to develop and deploy a modernized system is all at once, in a big-bang deployment. A big-bang deployment eliminates adapters, bridges, and other connectors. It eliminates concurrently fielding both modern and legacy components , and it reduces the number of testing cycles to one. Again, this is in theory.

In practice, big-bang deployments are almost impossible in a large-scale modernization effort. In the time it takes to develop a modern system from the ground up, the target has typically moved. So although the modern system may achieve the original objectives, they may no longer be valid. Also, it is extremely difficult to reproduce the functionality of a legacy system that has been refined over many years by user involvement and feedback, without having the advantage of some user participation. In most cases, incremental deployment is necessary to obtain user feedback without completely disrupting the organization.

Incremental development can mean the difference between success and failure in a modernization effort. Once a modernization plan has been developed, it must be validated . The best way to do this is by selecting a small but difficult increment and demonstrating the validity of the plan.

Finally, it is unlikely that any plan will be implemented without modification. When developing and deploying in increments, it is possible to learn from past increments to improve both the process and the product. In a big-bang deployment, any lessons learned would be learned too late to affect the outcome of the modernization effort.

Once the plan has been proved, it can be scaled up to production levels. Any number of concurrent development efforts can be implemented simultaneously ”limited only by the available resources.