We can define business rules as statements that are used by a body or an organization to run their activities. Some of these rules are drafted by the body itself, others are rules that have been drafted by external body but it will have an effect on the organization. Some business rules are documented explicitly, others are used implicitly. Globalization of business and increased competition cause frequent changes in business rules. New rules are added, old rules are modified or retracted. For example, to compete with its rivals, a bank should adjust its interest rate, launch new services etc. In this situation that is very hard to keep the rules consistency, there is the chance that some rule violate the other. Dealing with conflicting business rules is an important aim of our work. In addition there are also situations where a manager should take a decision although not all relevant information is known. He/she must be able to draw conclusions even if the available evidence is insufficient to guarantee their correctness. Obviously, such conclusions are risky and may be invalidated in the light of new, more accurate information. This situation is referred to as reasoning with incomplete information.