Date has claimed that the degree of normalization attained in a given analysis depends upon the level of granularity under consideration. At the level of relation variables, repeating groups are an evil fraught with perilous rivaling nulls. At the finer level of atomicity constituting an attribute, additional semantic content may become visible. In the following, sets of days are quite distinct from the constituent days that constitute those sets. Further, types are distinct from domains.
Types are values only, existing without regard to time or place, and remaining forever immutable.
Operations defined upon types constitute domains. No nulls anywhere. Each issue of the magazine focuses on providing practical, strategic solutions and useful information you can put to work every day. This is not true. You just need to use the correct tool.