Briefly, that image shows 18 tables, the Table (Excel Sheet) name is in the Title bar of each block.
Each block lists the Field (Excel Column) names. You can't see all the Fields in the blocks with scroll bars.
The lines represent Relationships, by field, between Tables.
Using the left side of the Orders Table:
- The top line, from Orders.Order ID to Order Details.Order ID, (I would have named Order Details as Order Items,) means that those two Fields have the same value in their respective Record (Excel Row).
- The Arrow on the Order Items Table end of the line means that there must be a Order Record before there can be an Order Item Record.
- The infinity symbol on the Order Items end means that there can be many Order Items Records (with the same Order ID) for each Order, but the 1 on the Orders end means that there can only be one Order Record for each Order Item Record.
- The lack of an arrow on the Orders Table means that there doesn't have to be a value in the Order Items ID field. (Order canceled, no items.)
Tables with only 2 fields are Index or Lookup tables (Excel Lookup tables)
Using Employees, Employee Privileges, and Privileges tables
- Employee Privileges is an Intermediate Index. It can contain many records with identical values in the Employee ID and Privilege Fields
- .
- Each of any employee's Records will contain only one unique Privilege ID value.
- Since many employees can have the same privilege, both Fields must be compared to uniquely identify a Record. (Both Fields have a Key symbol next to Them.)
- The Key symbol indicates a Table Key Field.
- A Table must have a Primary Key Field, and can have a Secondary Key Field, and in very rare cases, a Tertiary Key Field. Generally, if you think you need a Tertiary Key, you need to redesign the Database.
Tables have plural form names. Fields have singular form names. IMHO, the use of ID Field names that include the Table name should be avoided, except for Secondary Keys and Intermediate Index Tables. See: Privileges, Orders Status, and Order Details Status Tables.
Also, IMHO, the Products Table is over simplified, in that it fails to consider that a product may have several suppliers, for example; #2 pencils.
A Possible Products Database structure
In-House Products Table
- In-House Product ID
- Product In-House Details Fields
A Tertiary Keyed Intermediate Index Table
- In-House Product ID
- Supplier ID
- Supplier Product ID
Supplier Tables
- Supplier Details
- Product Table
Suppliers' Product Tables
- Product ID
- Product Detail Fields
I hope this helped.