%------------------------------------------------------------------------------------------------------------
%%% 使用句法信息的一些思考
\begin{tikzpicture}
{\small
\begin{scope}[xshift = -0.3in, sibling distance=3pt, level distance = 18pt]
\Tree[.S
        [.NP
            [.NNP \node(w1){Messi}; ]
        ]
        [.VP
            [.VBD \node(w2){hit}; ]
            [.NP
                [.DT \node(w3){the}; ]
                [.NN \node(w4){ball}; ]
            ]
        ]
     ]
\node [anchor=north west] (cap1) at ([yshift=-2.0em,xshift=2.0em]w1.south west) {\small{(a) 短语结构树}};

\node [anchor=west] (t1) at ([xshift=4em,]w4.east) {Messi};
\node [anchor=west] (t2) at ([xshift=0.5em,]t1.east) {hit};
\node [anchor=west] (t3) at ([xshift=0.5em,]t2.east) {the};
\node [anchor=west] (t4) at ([xshift=0.5em,]t3.east) {ball};

\draw [->] ([xshift=0em]t3.north) .. controls +(north:1em) and +(north:1em) .. ([xshift=-0.2em]t4.north);
\draw [->] ([xshift=0.2em]t4.north) .. controls +(north:2.5em) and +(north:2.5em) .. ([xshift=0.2em]t2.north);
\draw [->] ([xshift=0.0em]t1.north) .. controls +(north:2.5em) and +(north:2.5em) .. ([xshift=-0.2em]t2.north);

\node [anchor=north west] (cap2) at ([yshift=-0.2em,xshift=-0.5em]t2.south west) {\small{(b) 依存树}};
\end{scope}
}
\end{tikzpicture}