Let \(E_{1}\) and \(E_{2}\) be two entities in E-R diagram with simple single valued attributes. \(R_{1}\) and \(R_{2}\) are two relationships between \(E_{1}\) and \(E_{2}\) where \(R_{1}\) is one - many and \(R_{2}\) is many - many. \(R_{1}\) and \(R_{2}\) do not have any attribute of their own. How many minimum number of tables are required to represent this situation in the Relational Model ?
3
When mapping an E-R model, each strong entity becomes a table, a one-to-many relationship is absorbed as a foreign key on the many side, and a many-to-many relationship always needs its own table.
Entities: \(E_{1}\) and \(E_{2}\) give 2 tables.
\(R_{1}\) (one-many): stored as a foreign key in the table of the many side, so 0 extra tables.
\(R_{2}\) (many-many): needs a separate table holding both keys, so 1 extra table.
Total \(= 2 + 0 + 1 = 3\)
Check: 4 would wrongly give the one-many relationship its own table, and 2 or 1 cannot hold the many-many pairs.
Hence, 3.
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