SAP SD relationship tables of SO, Delivery & Invoice

SAP SD Relationship between sales order number, delivery number and billing number tables

VBELN is the field name in the tables of VBAK (sales order), LIKP (delivery) and VBRK (billing).VBFA table provides links between preceeding (sales document) and subsequent (delivery) documents.
in VBFA table a delivery can be a preceeding document to an invoice(subsequent document) 

Document number can be found within the transaction table.
in the delivery : field VGBEL contain the sales order number.
in the invoice : field VGBEL contain the delivery number & field VBELV contain sales order number.