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I'm used to tracking Critical Path as a way to manage a work stream. How do I do that using Lifecycle?
Lifecycle doesn't use the traditional "waterfall" concept of Critical Path. Instead, dependencies are tracked and managed so work flows continuously. Up front high-level planning is done to minimize dependencies between features. Then, detailed plans evolve over time just ahead of the next sprint/iteration.
One goal within Agile is to define features in a way that eliminates (or at least minimizes) dependencies between features, which gives the organization more flexibility in evolving the prioritized list of features. Sometimes, especially in large, complex projects, it may not be possible to eliminate all the dependencies between features.
Feature dependencies can be tracked within a project or even across projects in Lifecycle. Dependencies are visible during the scheduling process so that they can be taken into account when defining a workload for a sprint/iteration. Dependencies can also be made visible when viewing features throughout the application to monitor any scheduling shifts that might occur in the current project or other projects.