How to design relationships for variant data? Help me define the table relationships for data with multiple structures. I need to track leads. Leads come from multiple sources. Each lead source has its own data structure. I need advice representing this in a relational database.

Each record in the TABLE "Products Sold List" (defined below) has a lead source. The leads can come from Organizations, Doctors, Company Office, and Company Employees. Here are the different types of data that constitute a lead.


TABLE Organization:
   - Name -- TEXT

TABLE Doctor:
   - NPI# -- INTEGER (unique for each doctor. I planned on using this as primary key)
   - FirstName -- TEXT
   - LastName -- TEXT

TABLE Company Office:
   - Location -- TEXT

TABLE Company Employee:
   - Department
      -- one of {Sales, Technician, QA}. Note that the employee is not tied to an office.
         Office leads are leads that come from misc office staff at the various locations.
   - FirstName
   - LastName

Here is TABLE Products Sold List:
   - [misc fields]
   - PrescribingPhysicianNPI > many-to-one > Doctor.NPI
      -- "doctor that prescribed the product for the patient"
   - SalesRep > many-to-one > [Company Employee].PrimaryKey
      -- "Sales Rep credited for the sale. Needed for commissions calculation"
   - LeadSource > ???


Misc information:

The company offers incentives to leads (affiliate commission) and incentives to sales staff (sales commission). Leads coming from Organizations and Company Offices don't get paid affiliate commission. I am considering merging TABLE Company Office into TABLE organization and using "Office -- " as the data to track different offices (i.e.: Organization.Name = "Office -- Cincinnati"). Bad idea? Issues?
This might force a bit of change for your tables, but we do something like this at work:

Ensure each table has a int/guid primary key of some sort:

Organization Table

ID | Name
1  | MyOrganization


Then create a type-table to house your different LeadSource types:

LeadSourceTypeKey | Description
1                 | Organization
2                 | Company Office


Then on your ProductSoldList Table add 2 columns LeadSourceID and LeadSourceType

Then you can easily query the ProductSoldList TABLE and know which LeadSource to join back to:

SELECT *
FROM   [ProductSoldList] PL
       INNER JOIN [Organization] O
       ON PL.LeadSourceID = O.ID AND
          PL.LeadSourceType = 1
       INNER JOIN [Company Office] CO
       ON PL.LeadSourceID = CO.ID AND
          PL.LeadSourceType = 2