I guuss Equation 3.1 should read:

**Equation 3.1**

\[

\begin{array}{c|ccc}

Employee & FName & WorksIn & Mngr \\\\

\hline

1 & Alan & 101 & 2 \\\\

2 & Ruth & 101 & 2 \\\\

3 & Kris & 102 & 3

\end{array}

\]

\[

\begin{array}{c|cc}

Department & DName & Secr& \\\\

\hline

101 & Sales & 1 \\\\

102 & IT & 3

\end{array}

\]

In which case, the number of non-ID columns is 5, the same as the number of arrows in Equation 3.2. This is not a coincidence, since Equation 3.1 is an instantiation of Equation 3.2. In particular, each non-ID column represents the image of the ID column under a function, which is the instantiation of one of the arrows in Equation 3.2.

**Equation 3.1**

\[

\begin{array}{c|ccc}

Employee & FName & WorksIn & Mngr \\\\

\hline

1 & Alan & 101 & 2 \\\\

2 & Ruth & 101 & 2 \\\\

3 & Kris & 102 & 3

\end{array}

\]

\[

\begin{array}{c|cc}

Department & DName & Secr& \\\\

\hline

101 & Sales & 1 \\\\

102 & IT & 3

\end{array}

\]

In which case, the number of non-ID columns is 5, the same as the number of arrows in Equation 3.2. This is not a coincidence, since Equation 3.1 is an instantiation of Equation 3.2. In particular, each non-ID column represents the image of the ID column under a function, which is the instantiation of one of the arrows in Equation 3.2.