In UML sequence diagrams, there is the possibility to specify a synchronous call with a reply message.
Example (taken from https://en.wikipedia.org/wiki/Sequence_diagram)
When modelling that in mermaid-js, it renders "OKish":
However, the syntax is "strange" (because, for the reply, it uses is the notation for asynchronous messages)
sequenceDiagram A ->> B: m1 B --) A: m2
mermaid-js seems to propose closed arrows as default:
Synntax in mermaid-js:
sequenceDiagram A ->> B: m1 B ->> A: m2
I checked the UML 2.5.1 specification on page 577; there it reads:
I have found no explanation for "either an open or filled arrow head".I also checked PlantUML (at https://plantuml.com/en/sequence-diagram), it also uses the open arrows.
Question: Is it open to the modeler which arrow head to use without altering the semantics of the reply arrow? Is mermaid-js the only tool leaning towards closed arrows?