Which BPMN gateway type must always yield at least one chosen path?

The Complex Gateway is a type of gateway in BPMN (Business Process Model and Notation) that requires at least one of the outgoing paths to be taken. It allows for more advanced routing decisions based on multiple conditions that may not be easily represented by a simple exclusive or parallel logic. While it can handle complex conditions, the requirement that at least one path must be selected ensures that the process continues to move forward, preventing deadlocks or situations where all paths might be ignored.

In contrast, other gateway types have different rules. The Exclusive Gateway, for instance, chooses one outgoing path based on conditions but does not guarantee that at least one path must be taken; it may lead to a situation where no paths are selected if none of the conditions are met. The Event-Based Gateway, while useful for waiting on events, also does not mandate that a path is selected after a certain event occurs. The Parallel Gateway allows multiple paths to be taken simultaneously, again without any requirement that at least one path is selected in a traditional sense because it simply activates all outgoing paths.

Thus, the Complex Gateway's fundamental behavior is what makes it the only option that ensures a minimum of one leg in the process flow is always taken.