19. The method of claim 16 , wherein said invalid fragment is indicated to be invalid by an invalid attribute.
16. A method implemented by an apparatus for updating a previously supplied electronic document providing programming information related to broadcasting a plurality of television broadcast programs scheduled for broadcast in a program broadcasting system, wherein said previously supplied electronic document is stored in a client of the program broadcasting system and has a hierarchical structure based on a prescribed syntax, the hierarchical structure including an upper fragment and a plurality of lower fragments located below the upper fragment in the hierarchical structure to describe, for each of the scheduled television broadcast programs, a program identifier, a title, broadcast information and corresponding program content information, the method comprising: receiving at a provider of the program broadcasting system a request from said client for an updated version of said previously supplied electronic document; and supplying from the provider to said client an update document to update the previously supplied electronic document, the update document having a structure based on the prescribed syntax and including the upper fragment and an invalid element, the invalid element indicating that one of the lower fragments of said previously supplied electronic document is invalid, wherein said invalid fragment is identified by the invalid element to be deleted from the previously supplied electronic document, and the invalid fragment is related to one of the television broadcast programs scheduled for broadcast in the program broadcasting system.