Mysql – Referential Integrity in schema, cascading the renaming

Okay, so here's the data model I came up with.

PRODUCT -- to store product information and maintain parent-child hierarchy

id  NUMBER  "Primary Key Not Null"                  
level_code  VARCHAR2    Not Null                    
name    VARCHAR2    Not Null                    
description VARCHAR2                        
parent_id   NUMBER  Foreign Key references PRODUCT(id)                  

ORDERS -- to store orders for products

id  NUMBER  "Primary Key Not Null"                  
prod_id     NUMBER  "Foreign Key references PRODUCT(id) Not Null"                   
order_type  VARCHAR2    "Not Null Default 'Default'"
order_qty   NUMBER  Not Null
order_date  NUMBER  Foreign Key references DATE_INFO(date_key)
delivery_date   NUMBER  "Foreign Key references DATE_INFO(date_key)
Check delivery_date >= order_date"

FORECAST -- to store forecast value for products (store value for higher levels, store value for lower levels after disaggregation from a parent)

id  NUMBER  "Primary Key Not Null"
product_id  NUMBER  "Foreign Key references PRODUCT(id) Not Null"
forecast_value  NUMBER  Not Null
week    NUMBER  "Foreign Key references DATE_INFO(date_key) Not Null"                   

DISAGGREGATION_RULES -- to store which method was used for disaggregating a value from a higher level to lower level and how much percentage got distributed to lower level

id  NUMBER  "Primary Key Not Null"
parent_product_id   NUMBER  "Foreign Key id references PRODUCT(id) Not Null"
child_product_id    NUMBER  "Foreign Key id references PRODUCT(id) Not Null"
method  VARCHAR2    Not Null                    
from_week   NUMBER  "Foreign Key references DATE_INFO(date_key) Not Null"
to_week NUMBER  "Foreign Key references DATE_INFO(date_key) Not Null Check end_week >= start_week"
percent_distribution    NUMBER  Not Null                    

DATE_INFO -- date dimension, has information about start date (has to be Saturday) and end date corresponding to the week in which a particular date falls

date_key    NUMBER  "Primary Key
Not Null"                   
full_date   DATE    Not Null                    
week_begin_date DATE    Not Null                    
week_end_date   DATE    Not Null

As for the bucket number .. I am calculating week start date (date on Saturday, in my case) with the following function

CREATE OR REPLACE FUNCTION get_week_start_date(v_bucket_num IN NUMBER)
  RETURN DATE
IS
  week_start_date DATE;
BEGIN
  SELECT (TRUNC(SYSDATE+2, 'IW')-2) + ((v_bucket_num-1) * 7)
  INTO week_start_date FROM dual;
  RETURN week_start_date;
END;

As you've identified, storing the price on the order makes the technical implementation easier. There are a number of business reasons why this may be beneficial though.

In addition to web transactions, many businesses support sales through other channels, e.g.:

• Over the phone
• Sales agents "on the road"
• At a physical location (e.g. shop, office)

In these cases the order may be entered into the system at some time after the transaction took place. In these circumstances it can be difficult to impossible to correctly identify which historical price record should be used - storing the unit price directly on the order is the only feasible option.

Multiple channels often bring another challenge - different prices for the same product. Surcharges for phone orders are common - and some customers may negotiate themselves a discount. You may be able to represent all possible prices for all channels in your product schema, but incorporating this into your order tables can become (very) complex.

Anywhere that negotiation is allowed it becomes very difficult to link price history to the order price agreed (unlesss agents have very narrow negotiation limits). You need to store the price on the order itself.

Even if you only support web transactions and having a relatively simple pricing structure, there's still an interesting problem to overcome - how should price increases be handled for in flight transactions? Does the business insist that the customer must pay increases or do they honour the original price (when the product was added to the basket)? If it's the latter it the technical implementation is complicated - you need to find a way to ensure you're maintaining the price version in the session correctly.

Finally, many businesses are starting to use highly dynamic pricing. There may not be one fixed price for a given product - it is always calculated at runtime based on factors such as time of day, demand for the product and so on. In these cases the price may not be stored against the product in the first place!