Creating the data structures for the database is the third phase in the database-design process. You define tables and fields, establish keys, and define field specifications for every field.
Tables are the first structures you define in the database. You determine the various subjects that the tables will represent from the mission objectives you wrote during the first phase of the design process and the data requirements you gathered during the second phase. Then you establish these subjects as tables and associate them with fields from the field list you compiled during the second phase of the design process. After you've completed this task, you review each table to ensure that it represents only one subject and that it does not contain duplicate fields.
Now you go on to review the fields within each table. You refine all multipart or multivalued fields in the table so that they each store only a single value, and you move or delete fields that do not represent distinct characteristics of the subject the table represents. When you complete this review, you then review and refine the table structures. This involves checking the work you performed on the fields to ensure that you didn't accidentally miss anything, and ensuring that each table structure is properly defined. Next, you establish the appropriate keys for each table. Your main task is to ensure that each table has a properly defined primary key; this particular key uniquely identifies each record within a table.
The final step in this phase is to establish field specifications for each field in the database. Here you conduct interviews with users and management to help you identify the specific field characteristics that are important to them and review and discuss any characteristics with which they may be unfamiliar. After you've completed these interviews, you define and document field specifications for each field. You then review the table structures and field specifications with users and management once more for possible refinements. The table structures are ready for the next phase once you complete the refinements (if any) that you identified during the review.