anchor.diff:  	when
   		ProductID :: string(),
   		Result :: ok.
  -%% @doc Delete an entry form the product table
  +%% @doc Delete an entry from the product table.
   delete_product(ProductID) ->
   	F = fun() ->
   		mnesia:delete(product, ProductID, write)
  
positive.code: 
  -spec get_products() -> Result
  	when
  		Result :: [#subscriber{}] | {error, Reason},
  		Reason :: term().
  %% @doc Get all entries in the product table.
  get_products() ->
  
negative.code: 		Product :: #product{},
  		Result :: ok | {error, Reason},
  		Reason :: term().
  %% @doc Add a new entry in product table.
  add_product(Product) ->
  	F = fun() ->
  		mnesia:write(product, Product, write)
  