What's the best way to represent a message that doesn't get received in a sequence diagram?

Question

I am trying to define a sequence that occurs when a message is missed in my system. What's the best way to do that with PlantUML?

The website http://www.uml-diagrams.org/sequence-diagrams.html#lost-message indicates a closed circle means a message was lost, but I don't see a way to do that in PlantUML.  Is the purpose of ->o to indicate a lost message?

Answer 1

Perhaps not the best way, but you could try:

skinparam style strictuml

boundary " " <<Lost>>

Bob->Alice : hello
Bob ->o " "

 

 

http://www.planttext.com/planttext?text=AyxEp2j8B4hCLIWkgSn91P95cSabfRavN4dvfNafYKML2af0Q6FZarzSOcV7vPIVf6ldc9EPdAfWfP2HcfEJ3n9IqBNB1wa30000 

Answer 2

Good idea Fuhrmanator! If you want to get away with the "Lost" participant, you may try incoming/outgoing message syntax:

           Bob ->o]
or
           [<-o Bob

The last one has a bug when going leftside, since it should logically be  [o<- Bob

Rem: Should we ask for a new arrow ending letting us represent a UML's lost message ?
This new ending would generate a filled circle. What syntax? Maybe   ->*  ?

And instead of having the arrow going outside the diagram with the in/out message syntax, maybe we could introduce a new syntax for lost message, for example  Bob ->*)   or  Bob ->*[  ??

 

Comments

The asterisk '*' is used to denote multiplicity in many UML diagrams so I would suggest some other character, maybe an 'o'?

Answer 3

Thanks for the suggestions.

I tried both of those, but what I wound up using was:

    src ->o dest: Message

I decided the open circle looked like the message didn't quite hit its target, but I could still see what the intended destination was. Using the "Lost" boundary or sending a message to the side of the page made it more visually obvious that the message was not received, but completely lost indication of the destination, which was important for my diagram.

 

 

 

Answer 4

Ok, here's another try (remembering how objects die...):

src ->x dest: Message

Comments

I like it!
It's not UML strict, but it's more understandable.

Note: the webpage about incoming/outgoing message syntax (sequence.html#inout) would need an update to document such arrow ending.

---

Sure, we will update the sequence.html page!

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Thank you for the update on the html page.

BTW, to be on par with the other arrow endings wrt to incoming and outgoing message, could it be possible to have the following syntax (with optional message text) ?

  [-x
  x-]

  src -x]
  [x- src

---

Good idea!

In the following beta https://dl.dropboxusercontent.com/u/13064071/plantuml.jar

You can have:

@startuml
Alice ->]
[-> Alice
Alice ->o]
[->o Alice
Alice ->x]
[->x Alice
Alice x<-]
[x<- Alice
@enduml

Is this what you were expecting ?
Thanks,

---

Exactly, many thanks!

Answer 5

Arrows that use "o" now have a filled circle by default (added with PR #1863, which is already merged and will be released with v1.2024.7 maybe?). So you can display lost and found messages by using e.g. the following code.

@startuml
participant ": A" as a
[o-> a ++ : method(key : char)
[o<<-- a : method(dir : String) : ret
@enduml

If you want to have a different fill color, you can use a style definition as follows.

@startuml
<style>
sequenceDiagram {
arrow {
BackgroundColor Blue;
}
}
</style>
participant ": A" as a
[o-> a ++ : method(key : char)
[o<<-- a : method(dir : String) : ret
@enduml