1. A security system for protecting a physical installation, the security system comprising: an access controller for controlling access to the physical installation comprising access control rules; a plurality of physical sensors in communication with the controller, wherein the plurality of physical sensors sense physical threats to the physical installation; a sensor report aggregator connected to the plurality of sensors and in communication with the access controller; and a security reference model connected to the sensor report aggregator, wherein the security reference model contains information about the protected physical installation including information about the protected physical installation's security goals; wherein the sensor report aggregator outputs hypotheses descriptive of a threat situation based on combined reports from the plurality of sensors to the access controller.