Author Question: How is a composite attribute of an entity mapped into a relation? What will be an ideal ... (Read 70 times)

bcretired · **on:** Jul 7, 2018

How is a composite attribute of an entity mapped into a relation?

What will be an ideal response?

Question 2

What is a primary key?

What will be an ideal response?

31809pancho · **Reply #1 on:** Jul 7, 2018

Answer to Question 1

If an entity contains composite attributes, each component of the composite attribute is mapped as a column of a relation, while the composite attribute itself does not appear in the mapped relation.

Answer to Question 2

Primary key is a column (or a set of columns) whose value is unique for each row. Primary keys cannot have null values. If there are multiple columns (or sets of columns) that have unique values in each row, one of them is designated as a primary key. Each relation must have a primary key.