schema design 2

Normal forms are a guidance to avoid known problems during schema design. Given a schema, whether we decompose it into smaller schema is determined based on this normal forms.  The normal forms are based on functional descriptors and are first normal form, second normal form, third normal form and Boyce Codd normal form. Each of these forms have increasingly restrictive  requirements. A relation is first normal form if every field contains atomic values and not lists or sets. 2NF is mainly historical interest. 3NF and BCNF are important from design standpoint. Boyce Codd Normal form for a relation R holds truie if for every FD X->A that holds over R, one of the following statements is true.
A belongs to X : that is, it is a trivial FD or
X is a superkey
Third normal form holds when for every FD X-> A that holds over R, one of the following statements is true:
A belongs to X : that is, it is a trivial FD or
X is a superkey or
A is part of some key for R