Bob,

1st NF addresses multivalued fields like a phone number field in a person table where there may be many phone numbers for each person. When you start to create Phone1, phone2, phone3 etc then you are in violation of 1st NF. 2nd NF addresses the dependency of data fields on the Primary key and states that the values of all fields must be dependent on the whole primary key and not only part of it (this is an issue when the PK has more than one field in it). 3rd NF says the fields are dependent on ONLY the PK for their values and not on any other fields except for alternate Keys.

In view of these definitions then deciding to forgo a look up table for a certain value is not an issue of normalization but rather an issue of other relational design criteria.