The chapter opened with a discussion of the importance of keys. You learned that there are different types of keys, and each type plays a different role within the database. Each key performs a particular function, such as uniquely identifying records, establishing various types of integrity, and establishing relationships between tables. You now know that you can guarantee sound table structure by making certain that the appropriate keys are established for each table.
We then discussed the process of establishing keys for each table. We began by identifying the four main types of keys: candidate, primary, foreign, and non-keys. First, we looked at the process of establishing candidate keys for each table. You learned about the Elements of a Candidate Key and how to make certain that a field (or set of fields) complies with these elements. Then you learned that you can create and use an artificial candidate key when none of the fields in a table can serve as a candidate key or when a new field would make a stronger candidate key than any of the existing candidate key fields.
The chapter continued with a discussion of primary keys. You learned that you select a primary key from a table’s pool of candidate keys and that the primary key is governed by a set of specific elements. We then covered a set of guidelines that help you determine which candidate key to use as a primary key. Next, you learned how to ensure that the chosen primary key exclusively identifies a given record and its set of field values. When the primary key does not exclusively identify a particular field value, you know that you must remove the field from the table in order to ensure the table’s structural integrity. You also know that each table must have a single, unique primary key.
You then learned that you designate any remaining candidate keys as alternate keys. These keys will be most useful to you when you implement the database in an RDBMS program because they provide an alternate means of identifying a given record. We then discussed the non-key field, which is any field not designated as a candidate, primary, alternate, or foreign key. You now know that a non-key field represents a characteristic of the table’s subject and that the primary key exclusively identifies its value.
Table-level integrity was the next subject of discussion, and you learned that it is established through the use of primary keys and enforced by the Elements of a Primary Key.
The chapter closed with some guidance on conducting further interviews with users and management. You now know that these interviews provide you with a means of reviewing the work you have performed on the tables and help you to verify and validate the current database structure.