The Usefulness of the Use Case?

re: The Usefulness of the Use Case?

Guy — Wed, 18 Jun 2008 05:48:44 GMT

Very insightful, this is very much in line with what I am working on right now, I agree with you completely.

What is the name of the "published work" that defines the process for creating clean and useful business rules? I'm interested in looking into it...

re: The Usefulness of the Use Case?

NickMalik — Wed, 18 Jun 2008 09:30:00 GMT

Hello Guy,

I'm going to recommend the following book on reputation alone.

Caveat: I have not read it (yet... I plan to):

"Business Rules Applied: Building Better Systems Using the Business Rules Approach" by Barbara Von Halle

I hope this helps.

--- Nick

re: The Usefulness of the Use Case?

Evan — Wed, 18 Jun 2008 17:47:39 GMT

We have to remember that the Use Case is only good for analysis. Juval, Fowler, etc all agree that the functional decomposition provided by the Use Case yields the worst design possible when translated directly to code. Even Parnas argues that a functional decomposition is a very poor design.

Knowing this, it's up to us to take the functional decomposition (which was used to analyze and understand the problem and desired solution) to create a proper design.

During the process of design (even if it only occurs inside my head), I break "business rules" or "business logic" into two categories: application logic and business logic.

The roots for both come from Fowler and Evans (DDD), where application logic might be something like: Send an email to the customer after accepting their order. Business logic is more along the lines: Calculate sales tax on orders shipping to CA or NY. The application logic represents a workflow that occurs (with/without any workflow framework) during the execution of a business goal (ConvertCartToOrder) and exists in the Service Layer facade (Fowler). The business logic exists in the domain model and is part of the emulation that occurs to manipulate the state space (objects/data) to work out the desired effect.

And that's basically it in a nutshell.

So, back to your original question. Are Use Cases useful? Yes, but only for gaining understanding by analyzing the problem space. Translating them beyond that is a known anti-pattern (which is agreed upon by multiple schools of thought).

re: The Usefulness of the Use Case?

NickMalik — Wed, 18 Jun 2008 18:44:25 GMT

It's interesting, Evan, that you appear to regard the process of eliciting business rules as a step between use case analysis and design. Many folks argue that business rules elicitation occurs BEFORE the use cases are described. I believe that these two steps are concurrent. Perhaps it doesn't matter?

I'm on the fence about the usefulness of separating rules into "business logic" and "application logic" as you describe. I understand what you are doing, but I'm not sure that doing it increases quality. I'd love to see actual experiments along those lines.

Anyway, I appreciate the discussion. Thank you for contributing your insight and experience.

re: The Usefulness of the Use Case?

David Wright — Thu, 19 Jun 2008 06:54:52 GMT

Much agreed, Use Cases can not do it all. I have presented on this topic a few times, and wrote the following: http://searchsoftwarequality.techtarget.com/tip/0,289483,sid92_gci1252666,00.html?track=NL-498&ad=588081&asrc=EM_NLN_1374391&uid=3080496#

Business Rules are a big deal, see http://www.businessrulesgroup.org/home-brg.shtml for the first and last word on Business Rules. I recommend Ron Ross as an author of several books on Rules.