%&tex
\documentclass{standalone}
\usepackage{tikz}
\usepackage{siltex}
\usetikzlibrary {arrows.meta,positioning,calc,math}
\tikzset{nodes={text height=.7em, text width=1.6cm, align=center,
draw=black!50, thick, font=\footnotesize, fill=white},
>={Stealth[round,sep]}, rounded corners, semithick}
\pgfdeclarelayer{bg}
\pgfsetlayers{bg,main}

\begin{document}
\begin{tikzpicture}[on grid,y=2.0cm,x=2.0cm]
    \node (re) {Requirement};
    \node (fu)[below right=1 of re]  {Function};
    \node (co)[below left=1 of re]  {Component};
    \begin{scope}[nodes={draw=none, auto, fill=none, midway,text width={},text height={}}]
        \path[->,line width=0.3mm] (re) edge node[right=2mm] {Specifies} (fu)
                  (co) edge node[below=3mm] {Performs} (fu)
                  (re) edge node[left=2mm] {Specifies} (co);
    \end{scope}
    \begin{pgfonlayer}{bg}
       \draw[fill=lightgray] (-1.3,0.25) rectangle (1.3,-1.1);
    \end{pgfonlayer}
\end{tikzpicture}
\end{document}
