Wednesday, November 11, 2009
Business Rules
Business Rules
A business rule is a
company policy, an industry standard, or a law or government regulation
that defines, constrains, or governs some aspect of the business. Most
business rules exist independently from a specific software system. For
this reason, I recommend that you document your business rules
separately from the requirements specification for a particular
product. Treat your business rules as an enterprise-level asset, not a
project-level asset. This facilitates reusing the rules, as they're
likely to apply to multiple projects and products. A business rules
catalog is a convenient place to collect the rules that affect your
applications if they aren't
already documented somewhere else, such as in a body of laws. Several
comprehensive books on business rules have been published in recent
years (Ross 2003; Morgan 2002; von Halle 2002). See Chapter 9 of Software Requirements, Second Edition for more about business rules.
Business rules would apply even if the business
processes were being performed manually instead of with the help of
software. This is one way to distinguish a rule from a software
requirement. As an illustration, I borrow a lot of movies on DVD from
my local library. If a movie I want to see isn't available immediately,
I put my name on the waiting list and eventually I reach the top of the
list. Once when I tried to request a movie, the library's Web site
displayed an error message: "Sorry, your library only allows you to
have 10 items on reserve at one time. Your reserve list already has 10
items, so you can't reserve this item now." The software was enforcing
a library policy—a business rule. That same policy applied long before
the library used computers, when librarians kept track of reserve lists
manually. The business rule thus has an existence outside the scope of
any particular library software application.
Even if you aren't building business applications,
your products could be subject to business rules in the form of
government regulations and industry standards. Electrical products that
contain embedded software might require Underwriters Laboratories
certification. To obtain this certification, the products must comply
with specific safety standards, which constitute a set of business
rules. Products that require certification by government bodies such as
the U.S. Food and Drug Administration are subject to business rules in
the form of laws and regulations. If your product doesn't conform to
the pertinent rules, the federal government won't approve it for sale
in the United States.
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