Which of the following is NOT a kind of control node?

A control node is a special type of node in a modeling language, such as UML (Unified Modeling Language), which is used to control the flow of control in activity diagrams. The primary function of control nodes is to manage the flow of execution or data within a model, directing the sequence of actions and decisions.

The initial node, merge node, and fork node are all types of control nodes that serve specific purposes. The initial node represents the starting point of a control flow in an activity diagram, the merge node is used to bring together multiple flows into a single flow, and the fork node is utilized to split a flow into multiple concurrent flows, thereby facilitating parallel processing.

In contrast, an object node is not categorized as a control node. Instead, it is used to represent an object or data element that is manipulated within the control flow. Object nodes carry information and can serve as inputs or outputs in an activity but do not control the execution of the flow itself. This distinction highlights why the object node does not fit within the classification of control nodes, making it the correct answer to the question about which is not a kind of control node.