These are the Steps in a Top-Down Approach :-
1 Define the Scope as the Area of Interest,(e.g. the HR Department in an organization).
2 Define the "Things of Interest",(e.g. Employees), in the Area of Interest.
3 Analyze the Things of Interest and identify the corresponding Tables.
4 Consider cases of 'Inheritance', where there are general Entities and Specific Entities.
For example, a Customer is a General Entity, and Commercial Customer and Personal Customer would be Specific Entities. If you are just starting out, I suggest that you postpone this level of analysis.
5 At this point, you can produce a List of Things of Interest.
6 Establish the relationships between the Tables.
For example, "A Customer can place many Orders", and "A Product can be purchased many times and appear in many Orders."
7 Determine the characteristics of each Table,(e.g. an Employee has a Date-of-Birth).
8 Identify the Static and Reference Data, such as Country Codes or Customer Types.
9 Obtain a small set of Sample Data,
e.g. "John Doe is a Maintenance Engineer and was born on 1st. August, 1965 and lives at 22 Woodland Street, New Haven.
"He is currently assigned to maintenance of the Air-Conditioning and becomes available in 4 weeks time"
10 Review Code or Type Data which is (more or less) constant, which can be classified as Reference Data.
For example, Currency or Country Codes. Where possible, use standard values, such as ISO Codes.
11 Look for 'has a' relationships. These can become Foreign Keys, or 'Parent-Child' relationships.
12 You need to define a Primary Key for all Tables.
For Reference Tables, use the'Code' as the Key, often with only one other field, which is the Description field.
I recommend that names of Reference Data Tables all start with 'REF_'.
For all non-Reference Data Tables, I suggest that you simply assign an Auto-increment Integer for each Primary Key.
This has some benefits, for example, it provides flexibility, and it's really the only choice for a Database supporting a Web Site.
However, it complicates life for developers, which have to use the natural key to join on, as well as the 'surrogate' key.
It also makes it possible to postpone a thorough analysis of what the actual Primary Key should be. Which means, of course, that it often never gets done.
13 Confirm the first draft of the Database design against the Sample Data.
14 Review the Business Rules with Users,(if you can find any Users).
15 Obtain from the Users some representative enquiries for the Database,
e.g. "How many Maintenance Engineers do we have on staff coming available in the next 4 weeks ?"
16 Review the Results of Steps 1) to 9) with appropriate people, such as Users, Managers,
17 Development staff, etc. and repeat until the final Database design is reached.
18 Define User Scenarios and step through them with some sample data to check that that Database supports the required functionality.
