RDBMS

• A relational database is well designed if you can reconstruct the predicates (and propositions) used to describe the business problem.
• Normalization is a redesign process to unbundle the entities. The process involves decomposition but not decomposition that leads to a loss of information.
• The goal of normalization is to eliminate redundancy and incompleteness.
• The first normal form (1NF) says that a table is in fi rst normal form if all columns are atomic. No multivalued columns are allowed. Note that the 1NF defi nition simply states that a table must represent a relation.
• Second normal form (2NF) a table must be in 1NF and every nonkey column must be functionally dependent on the entire key that means decomposition means creating new tables, not just new rows like in 1NF. To achieve 2NF, you need to decompose the table into two or more tables.
• third normal form (3NF) a table must be in 2NF, and every nonkey column must
  be nontransitively dependent on every key. In other words, nonkey columns must be mutually independent. (Example)
• Boyce-Codd normal form (3.5 NF): It is stronger version of 3NF. A 3NF table which doesn't have multiple overlapping candidates keys is guaranteed to be in BCNF. If A--->B and A--->C but B and C are unrelated, ie A--->(B,C) is false, then we have more than one multi-valued dependency.
• Ref: http://support.microsoft.com/kb/283878