I do not know the key

Question

I use:

\documentclass[hyperref={unicode,bookmarks=true}, clock,fragile]{beamer}
\usepackage{amsmath,amssymb,amsfonts, mathrsfs}
\usepackage[utf8]{vietnam}
\usepackage{tikz,tkz-tab,pgf}
\usepackage{pgfplots}
\usetikzlibrary{arrows,decorations,decorations.pathmorphing,
shapes}
\usetikzlibrary{arrows,decorations,decorations.pathmorphing,
shapes,decorations.text,trees,positioning,datavisualization}
\usepackage{pgfcore}
\usepgflibrary{datavisualization.formats.functions}
\usetheme{Darmstadt}
\usetheme{CambridgeUS}
\begin{document}
\begin{frame}
\begin{tikzpicture}[baseline]
\datavisualization [ scientific axes=clean,
y axis=grid,
visualize as smooth line/.list={sin,cos,tan},
style sheet=strong colors,
style sheet=vary dashing,
sin={label in legend={text=$\sin x$}},
cos={label in legend={text=$\cos x$}},
tan={label in legend={text=$\tan x$}},
data/format=function ]
data [set=sin] {
var x : interval [-0.5*pi:4];
func y = sin(\value x r);
}
data [set=cos] {
var x : interval [-0.5*pi:4];
func y = cos(\value x r);
}
data [set=tan] {
var x : interval [-0.3*pi:.3*pi];
func y = tan(\value x r);
};
\end{tikzpicture}
\end{frame}
\end{document}

But when run pdfLatex I get"! Package pgfkeys Error: I do not know the key '/tikz/data visualization/style sheet'" How to fix it? Thanks.