What distinguishes a platform event from an event message?

A platform event is indeed recognized as a type of notification used in Salesforce’s event-driven architecture, designed for delivering real-time information. The essence of this distinction lies in the roles they play in communication processes. The term "platform event" refers to the predefined structure the developer creates, which acts as a template for the form and type of messages that can be sent. Meanwhile, an "event message" refers specifically to the actual data payload—the content—that is pushed through the event framework when an event occurs.

This means that when a platform event is fired, it generates an event message which contains the actual data pertaining to that occurrence. In this sense, platform events serve as a framework, while event messages are the real-time notifications containing relevant information, making them closely linked but distinct in function.

The other choices do not accurately encapsulate this relationship or mischaracterize the definitions and purposes of platform events and event messages. For instance, defining event messages as a specific kind of Salesforce object does not reflect their operational role, while the idea that they are stored in the user interface misrepresents how these elements function within the Salesforce ecosystem.