SplittingThe processes of grooming and splitting user stores (when needed) are ongoing operations across the life of the any project.  Epics and larger stories are ground down into smaller pieces that they can be understood and developed within the context of an individual sprint.  The backlog of user stories needs to be managed so that, as a story gets closer to being accepted into a sprint and developed, the story becomes as granular as needed.

Stories, when they are accepted into a sprint, must meet the “rule.” The rule is that each story must deliver functionality that is potentially implementable.  I strongly suggest that this rule is only rule that can’t be broken.  Breaking this rule tends to create waterfall or architectural splits, which flies in the face of the Agile principles.  The guidelines inferred by the INVEST acronym provide a directional framework to create well-formed stories.

When teams need direction about how to spilt stories, there are any number of patterns. Some are functionally oriented and some non-functional (rather, they are architecture). All of the stories created should be thin slices of deliverable functionality and have value.  Anything else might work, but fails to rise to the level the Agile principles suggested for delivery of valuable software.