mar/graphics/functional_relation.tex

%&tex
\documentclass{standalone}
\usepackage{tikz}
\usepackage{siltex}
\usetikzlibrary {arrows.meta,positioning}
\tikzset{nodes={text height=.7em, text width=2.5cm, align=center,
draw=black!50, thick, font=\footnotesize},
>={Stealth[round,sep]}, rounded corners, semithick}

\begin{document}
\begin{tikzpicture}[on grid,y=2.2cm,x=5.7cm]
    \node (re) {Requirement};
    \node (fu)[right=1 of re]  {Function};
    \node (co)[above=1 of fu]  {Component};
    \begin{scope}[nodes={draw=none, auto, fill=none, midway,text width={},text height={}}]
        \path[->] (re) edge node[below] {Specifies} (fu)
                  (co) edge node {Performs} (fu)
                  (re) edge node {Specifies} (co);
    \end{scope}
\end{tikzpicture}
\end{document}