Significance of VE04

Can anyone tell me the significance of VE04. What is the difference between Internal and External numbers. The way I understood it external number is the number assigned by the customer to your company (say his vendor number). Internal number is the number assigned by your company to the partners (ex:bp, sh) for a particular customer for that external number. I know its little messy but If someone can briefly explain to me about external and internal number it will be of great help to me.

Regards,

Shirish