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THE BUSINESS RULES PARADIGMThe concept of business rules has been used in infor-mation systems for some time. There are many software products that help organiza-tions manage their business rules (for example, JRules from ILOG, an IBM company).In the database world, it has been more common to use the related term integrity con-straintwhen referring to such rules. The intent of this term is somewhat more limitedin scope, usually referring to maintaining valid data values and relationships in thedatabase.A business rules approach is based on the following premises:• Business rules are a core concept in an enterprise because they are an expression ofbusiness policy and guide individual and aggregate behavior. Well-structuredbusiness rules can be stated in natural language for end users and in a data modelfor systems developers.
64Part II•Database Analysis• Business rules can be expressed in terms that are familiar to end users. Thus, userscan define and then maintain their own rules.• Business rules are highly maintainable. They are stored in a central repository, andeach rule is expressed only once, then shared throughout the organization. Eachrule is discovered and documented only once, to be applied in all systems devel-opment projects.• Enforcement of business rules can be automated through the use of software thatcan interpret the rules and enforce them using the integrity mechanisms of thedatabase management system (Moriarty, 2000).Although much progress has been made, the industry has not realized all ofthese objectives to date (Owen, 2004). Possibly the premise with greatest potentialbenefit is “Business rules are highly maintainable.” The ability to specify and main-tain the requirements for information systems as a set of rules has considerablepower when coupled with an ability to generate automatically information systemsfrom a repository of rules. Automatic generation and maintenance of systems willnot only simplify the systems development process but also will improve the qualityof systems.Scope of Business RulesIn this chapter and the next, we are concerned with business rules that impact only anorganization’s databases. Most organizations have a host of rules and/or policies thatfall outside this definition. For example, the rule “Friday is business casual dress day”may be an important policy statement, but it has no immediate impact on databases. Incontrast, the rule “A student may register for a section of a course only if he or she hassuccessfully completed the prerequisites for that course” is within our scope because itconstrains the transactions that may be processed against the database. In particular, itcauses any transaction to be rejected that attempts to register a student who does nothave the necessary prerequisites. Some business rules cannot be represented in com-mon data modeling notation; those rules that cannot be represented in a variation of anentity-relationship diagram are stated in natural language, and some can be repre-sented in the relational data model, which we describe in Chapter 4.