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Chapter 9. Rules and Conditions

Chapter 9. Rules and Conditions

Software applies knowledge to data. This is true for all software from business applications to video games. The knowledge inside software is generally a combination of procedural knowledge and declarative knowledge. Procedural knowledge is information about how to perform a task, like how to make a car and hotel reservation using an electronic travel broker. Procedural knowledge is easy to express using a general-purpose programming language like C#, Visual Basic, or any of their predecessors.

Declarative knowledge, on the other hand, is about the relationships in data. We often refer to declarative knowledge as business rules. For example, a business rule might say that hotel reservations made at least 14 days in advance receive a 10% discount, unless the cost of the room is less than $100. The date and the price share a relationship and can affect each other. Expressing this type of knowledge using a general-purpose programming language isn't difficult on a small scale, but breaks down as the amount of knowledge grows. We must transform the knowledge into procedural code using if-then-else statements. Many software applications require an enormous number of business rules: tax preparation systems, mortgage-banking software, and hotel reservation systems, to name just a few.


  

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