Which diagramming technique shows actions and events in a horizontal flow?

The technique that effectively demonstrates actions and events in a horizontal flow is the Activity Diagram. Activity Diagrams are part of the Unified Modeling Language (UML) and are designed specifically to illustrate workflows or processes. They showcase how activities interact in a sequence, emphasizing the flow from one action to the next, typically represented in a linear or horizontal manner. This visualization makes it easier to understand the steps involved in a process and how they relate to one another.

Activity Diagrams utilize symbols such as ovals for start and end points, rectangles for actions, and arrows to indicate the flow of control from one activity to the next. This helps stakeholders comprehend not just the individual activities but also the overall progress and dependencies within a process.

In contrast, State Diagrams focus on the states of an object and the transitions between those states rather than the flow of activities. Sequence Diagrams, while also displaying interactions, do so across a timeline and emphasize the chronological order of messages exchanged between components rather than a straightforward flow of actions. Class Diagrams are centered on the structure of a system rather than processes, depicting classes and their relationships rather than events or actions in a flow pattern.