WebSequenceDiagrams Notation

https://www.websequencediagrams.com/ supports notation for synchronous calls, asynchronous calls, return calls and activations.  These features are useful for documenting complex interactions with some of the operations happening in the background.  The example below illustrates these interactions (see https://www.websequencediagrams.com/examples.html for full documentation).

Image:

Source:

title call flows  
  
a->+b: sync call  
b->b: in process call  
b->>+c: async call  
c-->b: 202 Accepted  
b-->-a: return value  
c->d: background process  
d->d:  
d-->-c: