ParentSpanID can either but NULL/empty or contain the 8 byte SpanID of the span that caused this span.
- A span without a ParentSpanID is called a “Root span”
- A span with a ParentSpanID is called a “Child span”
- Many spans can have the same ParentSpanID and they are all children of the parent
- A span can ONLY have one parent
- A child span can also a parent span that it spawns
|ParentSpanID in specs||specs/Trace/Span.ParentTraceID|
|ParentSpanID proto definition||specs/Trace/Span.ParentSpanID|