A method of processing a digital service signal, the method comprises: receiving current time information and application signaling information via a broadcast network for receiving an application from the digital service signal, wherein the application signaling information includes channel information associated with the application; generating a hypertext transfer protocol, HTTP, request sentence for receiving uniform resource locator, URL, information of the application related to a program of the digital service using the current time information and the channel information; sending the generated HTTP request sentence to a domain name system, DNS, server, wherein the DNS server has a data base including program information according to each channel, wherein the program information includes titles of programs of each channel, start time of the programs, end time of the programs and Uniform Resource Locator, URL, information of applications related to the programs, and wherein the DNS server detects whether the program is changed to another program using the program information and the current time information for transmitting another URL information of another application related to the another program; receiving the URL information of the application from the DNS server in response to the HTTP request sentence; downloading the application using the URL information from an application server, wherein the application is associated with an application programming interface, API, to set mode information indicating a display status of the application, wherein the mode information includes a mode number indicating the display status of the application and a key set to input information through an input device such as a remote controller, wherein the key set indicates keys which are needed in the display status of the application, wherein the key set is changed when the display status of the application is changed, and wherein the display status of the application is a full display or an icon display, wherein the full display indicates that actual contents of the application are displayed on a screen and the icon display indicates that only an indicator of the application is displayed on a screen; executing the application and the API to set the mode information; registering the key set according to the mode number; and processing an input signal according to the registered key set. receiving current time information and application signaling information via a broadcast network for receiving an application from the digital service signal, wherein the application signaling information includes channel information associated with the application; generating a hypertext transfer protocol, HTTP, request sentence for receiving uniform resource locator, URL, information of the application related to a program of the digital service using the current time information and the channel information; sending the generated HTTP request sentence to a domain name system, DNS, server, wherein the DNS server has a data base including program information according to each channel, wherein the program information includes titles of programs of each channel, start time of the programs, end time of the programs and Uniform Resource Locator, URL, information of applications related to the programs, and wherein the DNS server detects whether the program is changed to another program using the program information and the current time information for transmitting another URL information of another application related to the another program; receiving the URL information of the application from the DNS server in response to the HTTP request sentence; downloading the application using the URL information from an application server, wherein the application is associated with an application programming interface, API, to set mode information indicating a display status of the application, wherein the mode information includes a mode number indicating the display status of the application and a key set to input information through an input device such as a remote controller, wherein the key set indicates keys which are needed in the display status of the application, wherein the key set is changed when the display status of the application is changed, and wherein the display status of the application is a full display or an icon display, wherein the full display indicates that actual contents of the application are displayed on a screen and the icon display indicates that only an indicator of the application is displayed on a screen; executing the application and the API to set the mode information; registering the key set according to the mode number; and processing an input signal according to the registered key set.