The normal form  of a relation refers to the highest normal form 
condition that it meets, and hence indicates the degree to which it has
been normalized. Normal forms, when considered in isolation from other 
factors, do not guarantee a good database design. It is generally not 
sufficient to check separately that each relation schema in the 
database is, say in BCNF or 3NF. Rather, the process of normalization 
through decomposition must also confirm the existence of additional 
properties that the relation schemas, taken together, should possess. 
These would include two properties.

The lossless join or nonadditives join poperty,
The dependency preservation property.

The lossless or nonadditive join property guarantees that the spurious 
tuple generation problem does not occur with respect to the relation 
schemas created after decomposition.

The dependency presevation poperty, ensures that each functional 
dependency is represented in some individual relations resulting after 
decomposition.