In one aspect, a computing apparatus is configured to represent offer rules based on requirements for the detection of predefined types of events, and actions scheduled to be performed in response to the detection of each occurrence of the events. The events are processed independently from each other and are linked via prerequisite conditions to formulate the requirements of an offer campaign. In one embodiment, the requirements for the detection of the events are specified based on predetermined types of events, including a first type for an event specified for interaction with a first user when the first user performs an action as a result of a referral from a second user, and a second type for an event specified for interaction with the second user in response to the first user performing the action.