In BPMN, the graphical aspects of the notation have been organized into specific categories. To support the requirements for complexity in BPMN, additional variation and information can be added within the basic categories of elements without dramatically changing the basic look and feel of the diagram.
Elements in BPMN have typically numerous attributes defined for them. Some of the attributes are designed to separate elements types from one another. For example, EventType attribute defines whether the event is of type start, end, or intermediate. Attributes form a conditional hierarchy where attributes can have sub-attributes, but all attributes need not necessarily be defined.