1. 1NF requires that all attributes have atomic (indivisible) domains.

2. The nested relational model is an extension of the relational model in which domains may be either atomic or relation-valued. This allows a complex object to be represented by a single tuple of a nested relation-one-to-one correspondence between data items and objects.

3. Suppose the information to be stored consists of (i) document-title, (ii) author list (set of authors), (iii) date (day, month, year), and (iv) key-word-list (list-of-key words).

4. Example: A non-1NF document relation, doc.

5. The doc relation can be represented in 1NF, doc0, but awkward. If we assume the following multi-value dependencies (MVDs) hold:
title →→ author
title →→ keyword
title → day month year
we can decompose the relation into 4NF using the schemes:
(title, author)
(title, keyword)
(title, day, month, year)

6. But the non-1NF representation may be an easier-to-understand model (closer to user's view). The 4NF design would require users to include joins in their queries, thereby complicating interaction with the system.We could de ne a view, but we lose the one-to-one correspondence between tuples and documents.