Vertical division of an Event Model into independently implementable units. Three slice types: write slice (command triggered from UI/REST causes a state change → event), read slice (events influence a view — no state change), and automation slice (event integrates with another module and dispatches a command). Because events form the contract between slices, and write/read sides are independent thanks to CQRS, slices can be assigned to different developers and tracked like game levels (red=todo, yellow=in-progress, green=done) — a convenient progress view for management and a natural way to split Jira tasks.