compress=yes;
Backend, Server, Client;
Client<-: Hit;
Client=>Server;
symbol shape above [shape=def.actor, size=0.2, color=blue];
symbol ... below;
Server>>Backend: Query [refname=query];
Server<<Backend: Response;
symbol rectangle around [line.radius=2, fill.color=yellow,50, 
                         distance=5];
Client<=Server: Reply;
symbol cross rightof [align=centerline, color=red];

symbol arc leftof query [align=bottom, size=big, distance=-18, 
                         offset=3, fill.color=teal,50];
note: this [ fill.color=teal,50];
symbol rectangle around query [fill.color=violet,50, 
                               line.radius=2, 
                               adjust=-30,2,2,-2];

symbol rectangle around [fill.color=aqua,50, line.radius=2, 
                         adjust=-30,2,2,2];
