Table Relationships

Relationships are used to "normalize" your data. Some of the goals of normalization are:

1. To Eliminate Repeating Groups
   Make a separate lookup file for each set of related attributes, and give each table a primary key. For example, you may be recording contacts that you have with your clients. You should not store the contacts in the client database. Instead, you would move the contact information into a separate table and relate each row to the primary key in the Client table.

2. To Eliminate Redundant Data
   If an attribute depends on only part of a multi-valued key, remove it to a separate table. Let’s say each contact you have with a client is categorized (Telephone call, mail-out, personal visit, etc.). You should store the Contact-Types in a separate table and relate the Contacts to the contact-types.

3. To Eliminate Columns Not Dependent On Key
   If attributes do not contribute to a description of the key, remove them to a separate table. For example, suppose you are storing the Client's Employer Name, Employer Address, and Employer Phone Number. These attributes describe the client's place of work, not the client, so you should create an Employer table and remove the Employer information to this table, relating it to its Key from the customer table.

These are the first three forms of data normalization and are probably the ones you will apply most commonly to your database.

See Also

General Topics