What is the difference between a Rule and a Policy [closed]

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. 开发者_JAVA百科 Closed 11 years ago.

in the context of a database, we sometimes need to check values against some statements like "the customer name is non-empty" or "the customer number of purchases is positive"...

But do such statements constitute rules or policies ?

In general how would you define these concepts, their differences and relations ?

Thanks in advance.

---

I think I know what you're talking about; I've run into such distinctions before (even though the English words are not all that different) and here is how I think it plays out in most business computing areas.

A rule in such a context is something that--whether it's a structural fact or a business-imposed statement--will not change, or at least stands only a very small chance of changing. Most statements of the form "X cannot be null" represent rules. "Null" typically doesn't make much sense to a business user; usually you arrive at these rules by examining the way that your model is constructed. A change to a rule has far-reaching consequences to the way that your database and any supporting applications are built.

A policy is more like a business instruction. Preferred customers get 10% off may be a policy, but as you know, things like this tend to change. A change to a policy may impact the way your application works, but not its fundamental architecture or underpinnings.

Pragmatically speaking--and it sounds like you may already know this--you want to make policies relatively easy to change. Rules, while they may change, are typically more involved: changing a rule often requires changing code, UIs, mental models, ways of thought, and so on.

I hope this helps.

---

In the context of a database, I would argue that it's a rule to have a username, while it's a policy (potentially overridden by administrative or other approval) to allow customers to have a lower assigned discount if they have less than a set number of purchases.

Rule: All users must have a username.
Rule: All users must have a password.
Rule: All users must have a valid email address.
Rule: All users must have a valid credit card on file.
Policy: All users begin with a 0% discount rate on purchases.
Policy: All users are required to pay for shipping.

Rules are outward-facing statements backed by validation. Policies are internal rules backed by consequence.

It could be a policy that later on down the road, a user can change a username (depending on how the software was written), or that the discount and shipping rates assigned on signup may be adjusted to create customer opportunities.

In my estimation then, a rule requires hard validation, while a policy by nature is subject to intervention and/or manipulation.

HTH

Jared