Rule Discovery is also named Business Rules Modeling in the industry and has the focus to develop simple modeling artifacts like rule descriptions, business entity diagrams and business process maps. 

The purposes of Rule Discovery  are:

• To define the rule classification from the business process
• To attach decision point to business process activities and / or use case steps
• To define the rule sources for the discovery and the type of roadmap to support the knowledge acquisition.
• To formalize the rules using templates and business term and language understood by the business user
• To prepare the test data  for the rules
• To define the object model for the rules

If the business modeling activity is done during the Inception phase of the project you should leverage the previous artifacts like the conceptual data model and the decision point table.

The discovery activities  are conducted during the Elaboration phase of the project, but the same process is conducted even after the system has gone into production when there is a new business event, or when there is a need to modify the decision logic of the application.

The most unique aspect of the rules discovery phase is the perception of a business event as a set of decision-rich activities. We unravel a business event as a set of decisions and policies. We then dissect the decisions and policies into executable and precise business rules that guide the business event in a predictable and desirable manner.