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is it 16 ?

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Lets start from $F$.

Here we have $2$ attributes $c$ and $d$ and none of them are primary attribute so $\{c,d \}$ togather will be assumed as primary key.

$E$ is a weak entity which means that it does not have its own primary key. So it will use primary key of $F$ i.e. $\{c,d \}$ which means it will have $a,b,c,d$ as its attribute.

The reason you would create any entities with an $ISA$ relationship is to give the new entity additional attributes.But here we are not adding any additional attributes to $G$ so it will have $4$ attributes only i.e. $a,b,c,d$

Now $H$ is having $2$ attributes $g$ and $h$ and none of them are primary attribute so $\{g,h \}$ togather will be assumed as primary key.

Also $S$ is a M:N relationship so it will have primary keys of both $G$ and $H$ to form a relation between them i.e. it will have $4$ attributes $c,d,g,h$

$\therefore$ In total we will have $16$ attributes.

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