If you need to find the relationship between Purch Line and Sales Line you can use the following links between the fields:
SalesLine.InventTransId == PurchLine.InventRefTransId
SalesLine.InventRefId == PurchLine.PurchId
SalesLine.InventRefTransId == PurchLine.InventTransId
SalesLine.ItemId == PurchLine.ItemId
These relationships are valid if the field: purchLine.ItemRefType = InventRefType::Sales