\begin{tikzpicture}%[show background grid]
    \begin{class}[text width = 2cm]{TArg}{0, 0}
    \end{class}

    \begin{class}[text width = 2cm]{TGroup}{5, 0}
    \end{class}

    \begin{class}[text width = 2cm]{TProgInit}{10, 0}
    \end{class}

    \begin{class}[text width = 2cm]{TProgram}{5, -2}
        \inherit{TProgInit}
        \inherit{TGroup}
        \inherit{TArg}
    \end{class}
\end{tikzpicture}
