A : In earlier days, business logic was generally implemented directly in the application code.Even today, many applications are built with business logic tightly coupled with the application code. This approach of rule implementation/ business logic implementation has lot of disadvantages and the biggest problem is tightly coupling.As a consequence, if there is a change in business logic,you need to make changes in all the areas which are impacted. Drools rule engine takes care of all the concerns discussed above.
So the new approach of using rule engines (like Drools rule engine, ILog JRules and many other) has emarged and revolutionized the business logic implementation. The biggest advantage is, decoupling the business logic implementation from the application code.The process of implementing and maintaining the business logic (rules) are much easier and quicker with rule engines.
Following are the advantages of Drools rule engine.
a) Declarative implementation : Rules/business logic is defined in a declarative way and it is much easier than writing them in application code.
b) Data and logic separation : This is again the advantage of decoupling the data and business logic (rules).
c) Speed, scalability and accuracy : Here the advantage comes from the efficient algorithms like Rete algorithm, Leaps algorithm etc.These are battle proven algorithms and perform efficiently, accurately and quickly.
d) Centralization of business logic : All the business logics/ rules are centralized. So it is easier to maintain/enhance/update.