\documentclass[11pt,a4paper]{book}
\usepackage{tikz}
\usepackage{pgf}
\tikzset{terminal/.style={
							% The shape:
							rectangle ,minimum size =6mm,rounded corners=3mm,
							% The rest
							very thick,draw=black!50,
							top color=white,bottom color=black!20,
							font=\ttfamily}}
\begin{document}
\begin{tikzpicture}[node distance=10mm]
	\node (dot) [terminal] {.};
	\node (digit) [terminal,right =of dot] {digit};
	\node (E) [terminal,right=of digit] {E};
\end{tikzpicture}
\end{document}