\begin{sequencediagram}
  \tikzstyle{inststyle}+=[{font=\large}]
  \def\unitfactor{.9}

  \newinst{instance 1}
  {instance 1}

  \newinst{instance 2}
  {instance 2}

  \newinst[4cm]{instance 3}
  {instance 3}

  \tikzstyle{instcolordienst}=[fill=black!25]
  \tikzstyle{instcolorbuerger}=[fill=black!25]

  \messcall{instance 3}{data 1}{instance 2}

  \begin{call}
    {instance 3}{data 2}
    {instance 2}{data 2*}

    \begin{callself}
      {instance 2}{Nutzerinteraktion}{data 3, data 2}
    \end{callself}

    \begin{call}
      {instance 2}{data 4, data 2}
      {instance 1}{}
    \end{call}
  \end{call}

\end{sequencediagram}
