A method of processing an interactive service at a receiver the method comprising: receiving uncompressed audio or video contents from an external decoding unit; extracting an identifier from a frame of the received content; sending a request having the identifier to a server; and receiving a trigger for the content from the server based on the request, downloading an application parameter table by using information in the trigger, the application parameter table including metadata about applications related to the content and events targeted to the applications, wherein the application parameter table includes a plurality of application elements, each of the application elements including metadata about a corresponding application, the metadata about the corresponding application including an application ID uniquely identifying the corresponding application within scope of the application parameter table, wherein the application element includes a plurality of event elements, each of the event elements including metadata about a corresponding event associated with the corresponding application, the metadata about the corresponding event including an event ID uniquely identifying the corresponding event within scope of the application element, wherein each of the event elements includes a plurality of data elements, each of the data elements including a corresponding data set to be used for a certain activation of the corresponding event and a data ID uniquely identifying the corresponding data set within scope of the event element, wherein the trigger is either a time base trigger or an activation trigger which sets a time for a specific activation of a specific event, the activation trigger including a first value, a second value and a third value, the first value referencing, within the application parameter table, an application ID of an application element representing an application targeted by the specific event, the second value referencing, within the application element referenced by the first value, an event ID of an event element representing the specific event, and the third value referencing, within the event element referenced by the first value and the second value, a data ID of a data element providing a data set to be used for the specific activation of the specific event. receiving uncompressed audio or video contents from an external decoding unit; extracting an identifier from a frame of the received content; sending a request having the identifier to a server; and receiving a trigger for the content from the server based on the request, downloading an application parameter table by using information in the trigger, the application parameter table including metadata about applications related to the content and events targeted to the applications, wherein the application parameter table includes a plurality of application elements, each of the application elements including metadata about a corresponding application, the metadata about the corresponding application including an application ID uniquely identifying the corresponding application within scope of the application parameter table, wherein the application element includes a plurality of event elements, each of the event elements including metadata about a corresponding event associated with the corresponding application, the metadata about the corresponding event including an event ID uniquely identifying the corresponding event within scope of the application element, wherein each of the event elements includes a plurality of data elements, each of the data elements including a corresponding data set to be used for a certain activation of the corresponding event and a data ID uniquely identifying the corresponding data set within scope of the event element, wherein the trigger is either a time base trigger or an activation trigger which sets a time for a specific activation of a specific event, the activation trigger including a first value, a second value and a third value, the first value referencing, within the application parameter table, an application ID of an application element representing an application targeted by the specific event, the second value referencing, within the application element referenced by the first value, an event ID of an event element representing the specific event, and the third value referencing, within the event element referenced by the first value and the second value, a data ID of a data element providing a data set to be used for the specific activation of the specific event.