Why PlantUML uses diamond for conditional in activity diagram?

Question

I am using plant UML to generate an activity diagram for my system information class. However, my lecturer said that my diagram is wrong. Because there should be no diamond shape in an activity diagram. She told me to search for a book or reference that explained why my activity diagram contains a diamond. Is there any book or reference that I could use to prove that the diamond shape is right? Or is Plant UML the wrong one here?

Below is a sample activity diagram with conditionals, notice that "more data?" is put inside a diamond (hexagon diamond).

Thank you!

Answer 1

PlantUML does not strictly follow the standard here.

However, there is a setting to go back in the right direction: skinparam conditionStyle diamond

@startuml
skinparam conditionStyle diamond
title Receive Loop
start
while (test) is ([connection open])
:Receive data;
while ( ) is ([data in receive buffer])
:Invoke decode;
:Handle decoder result;
endwhile ([else])
endwhile ([else])
end
@enduml

Is this what you are expecting ?