Digital television system channel guide having a limited lifetime

A method for receiving a plurality of digitally-encoded television programs wherein each of said digitally-encoded television programs is associated with at least one of a plurality of digital data transmission channels, each of said digital data transmission channels has the capacity to transmit at least one digitally-encoded television program and at least one of said plurality of digital data transmission channels includes television program schedule data, said method comprising:

• selecting a digital data transmission channel including television program schedule data from said plurality of digital data transmission channels, said television program schedule data being updated at predetermined time intervals and comprising:
• a first data structure defining the relationship of each of said television programs to respective ones of said plurality of digital data transmission channels,
• a second data structure indicative of a time period during which said defined relationships are valid, and
• a third data structure indicative of a change in said defined relationships;
• examining said second and third data structures of said television program schedule data of said selected digital data transmission channel, said third data structure being examined more frequently than said second data structure;
• acquiring and storing said first data structure of said television program schedule data of said selected digital data transmission channel if said examination of said second data structure indicates that said valid time period is less than a predetermined time period or if said examination of said third data structure indicates that said defined relationships have changed.