A field attains field-level integrity after you've defined a complete set of field specifications for the field. Field-level integrity warrants the following:
The identity and purpose of a field is clear, and all of the tables in which it appears are properly identified.
Field definitions are consistent throughout the database.
The values of a field are consistent and valid.
The types of modifications, comparisons, and operations that can be applied to the values in the field are clearly identified.
You can guarantee that a field structure is sound and optimally designed when it has a complete set of field specifications and fully conforms to the Elements of the Ideal Field. In fact, ensuring that the field complies with the Elements of the Ideal Field makes defining a set of specifications a relatively easy task.
If you've had any lingering doubt about a particular field's conformance to the Elements of the Ideal Field, now is a good time to review that field once more. If you determine that it is not in conformance, use the appropriate techniques to resolve the problem and make the proper adjustments to the table; otherwise, you can begin the process of defining field specifications for each field in the database. Here are the Elements of the Ideal Field once again for your convenience.
It represents a distinct characteristic of the subject of the table.
It contains only a single value.
It cannot be deconstructed into smaller components.
It does not contain a calculated or concatenated value.
It is unique within the entire database structure.
It retains a majority of its characteristics when it appears in more than one table.