Computed Values

Question

Like most people, I work on a data-driven object-oriented business application. I use a relational database to store my data.

I have designed my application so far that I never store computed values. That is, if a user would like to consult the output of a "simulation" he ran last year, my application would simply recompute the report from existing historical data, instead of reading the result of the simulation. Since the report takes very little time to create - it's mostly simple arithmetic - can I safely assume I can get by without storing the result of their reports? I'm having a hard time figuring out a future business requirement which would make me regret not having stored the results in the first place.

Answer 1

Tax changes, any other regulation that apply to All the data.

You can get around it by using values at the time, but when it involves any calculation that's changed complexity starts to build up.

Answer 2

If you have all the data you and can compute simulations based on that data then you should be fine. If in the future you find that these simulations are taking too long to run then you can begin storing the computed values and simply change your application to pull historical values from there.

Answer 3

Not storing the result of computations reduces redundancy and is generally, in my opinion, a good thing - but it comes down to a case of normalization vs. computational power required for an operation. Often, databases don't get 100% normalized because we don't live in the ideal world where that would be ideal (infinite CPU power and I/O speed), and so it should really be determined on a case-by-case basis.

If you can't foresee a need for storing the results of a computation in the DB, I'd suggest you don't store it. A DB is generally easier to maintain, the more normalized it is.