anchor.diff:  -record(alteration,
   		{name :: string(),
   		description :: string(),
  -		valid_for	:: {integer(), integer()},
  +		valid_for	:: valid_for(),
   		type :: price_type(),
   		units :: unit_of_measure(),
   		size :: integer(),
  
positive.code: -record(price,
  		{name :: string(),
  		description :: string(),
  		valid_for	:: {integer(), integer()},
  		type :: price_type(),
  		units :: unit_of_measure(),
  		currency :: string(),
  		period :: valid_period(),
  		size :: integer(),
  		amount :: integer(),
  
negative.code: -type price_type() :: recurring | one_time | usage.
  
  %% define unit of measure
  -type unit_of_measure() :: octets| cents | seconds | mb | gb.
  
  %% define validity period of a product
  -type valid_period() :: daily | weekly | monthly | yearly.
  
  -type valid_for() :: {SDT :: integer() | undefined, EDT :: integer() | undefined}.
  
  
  %% define client table entries record
  