The following EER diagrams illustrate specialization$/$generalization relationships.

Study the diagrams and answer the following questions.

a$)$ In Figure $1,$ is it $OK$ to change notation d to notation o$?$ Justify your answer.

b$)$ What is the difference between Figure $1$ and Figure $2?$ Explain the meaning clearly.

c$)$ One of these two diagrams $($Figure $1$ and Figure $2)$ can be converted into

union$/$category EER relationship, which one?

d$)$ Draw the union$/$category EER diagram that is converted from Figure $1$ or Figure $2$

$($your choice of previous question$).$