GATE CS 2008 Q82 — ER-model

To find the minimum number of tables required, we analyze the entities and relationships in the ER diagram:

1. Entity $M$ and Relationship $R1$: The arrow from $R1$ to $N$ indicates a many-to-one relationship from $M$ to $N$. Therefore, the relationship $R1$ can be merged into the table for $M$ by adding the primary key of $N$ ($N1$) as a foreign key.
   $$\text{Table 1: } M(\underline{M1}, M2, N1)$$
2. Entity $N$: This is a strong entity set and requires its own table.
   $$\text{Table 2: } N(\underline{N1}, N2)$$
3. Weak Entity $P$ and Identifying Relationship $R2$: $P$ is a weak entity set (indicated by the double rectangle) with a partial key $P1$ (dashed underline), and $R2$ is its identifying relationship (double diamond). A weak entity set and its identifying relationship are always merged into a single table containing the weak entity's attributes and the owner entity's primary key.
   $$\text{Table 3: } P(\underline{N1, P1}, P2)$$

Thus, a minimum of 3 tables are needed to represent the ER diagram.