1. A method of processing an interactive service at a receiver, comprising: receiving, by a receiving module, uncompressed content from an external decoding unit; extracting, by a signature module, a signature from a frame of the uncompressed content periodically; sending, by a network interface, a request including the signature to a server which checks the signature against a database of signatures; receiving, by the network interface, a trigger for the uncompressed content from the server, wherein whether the trigger is either a time base trigger or an activation trigger is determined by the server based on the frame represented by the signature, wherein the trigger is the time base trigger when no event activation is scheduled to take place before a next request, and wherein the trigger is the activation trigger when a specific event is due to be activated; and receiving, by the network interface, an application table including metadata about applications and events targeted to the applications, the application table including a plurality of application elements at top level of the application table, each of the application elements having an application ID identifying the each of the application elements within a scope of the application table, the each of the at least one application elements including a plurality of event elements as sub-elements of the each of the application elements, each of the event elements representing an event targeted to an application that the each of the application elements represents, the each of the event elements having an event ID identifying the each of the event elements within a scope of the each of the application elements; wherein the time base trigger includes a timestamp indicating current media time of the uncompressed content, wherein the activation trigger identifies the specific event to be activated from the application table and indicates an activation time for the specific event based on the media time, wherein the activation trigger includes an event term and a timing term, wherein the event term includes a first value referencing one of the application elements representing an application targeted by the specific event, and a second value referencing one of the event elements representing the specific event from the one of the application elements referenced by the first value, wherein the timing term indicates the activation time for the specific event, and wherein the activation trigger further includes a version term indicating a version of the application table with which the activation trigger is associated.