1. A method, comprising: receiving, by a computing device, first business logic expressed in one or more declarative languages, the first business logic including a first process description, the first process description describing a first process of a business process instance in terms of one or more flows; receiving, by the computing device, second business logic expressed in the one or more declarative languages, the second business logic including a second process description, the second process description describing a second process of the business process instance in terms of one or more rules, the second process being different from the first process; and executing, by the computing device, the first business logic and the second business logic, wherein the business process instance is associated with one or more states, wherein each of the one or more flows represents a control flow between business functions, wherein each of the one or more states represents a legal state transition for at least one business entity, and wherein each of the one or more rules represents a business rule or policy enforced on the at least one business entity in an externalized form.