1. In a server, a method for dynamically updating descriptions of audio-visual content information at a client, said method comprising: said server sending to said client a command indicating a type of update to make at a particular node of a data structure residing at said client and describing an item of content, wherein said particular node contains information describing an attribute of said item of audio-visual content and wherein said particular node is one of a plurality of nodes of said structure, wherein said plurality of nodes are associated with one another to form said structure; said server sending to said client the location of said particular node in said description; and said server retrieving and sending to said client any data related to said update, wherein said client executes said command and performs said update using Data Description Language (DDL).