are preferably stored in a matrix form that allows the system to efficiently identify a new set of media items that complements the input set of media items application_number US 201213674820 A description reference is now made to the figures in which like reference numerals refer to like elements for clarity the first digit of a reference numeral indicates the figure number in which the corresponding element is first used in the following description certain specific details of programming software modules user selections network transactions database queries database structures etc are omitted to avoid obscuring the invention those of ordinary skill in computer sciences will comprehend many ways to implement the invention in various embodiments the details of which can be determined using known technologies furthermore the described features structures or characteristics may be combined in any suitable manner in one or more embodiments in general the methodologies of the present invention are advantageously carried out using one or more digital processors for example the types of microprocessors that are commonly found in servers pc 39 s laptops pda 39 s and all manner of desktop or portable electronic appliances the system preferably comprises or has access to a knowledge base which is a collection of mediasets a mediaset is a list of media items that a user has grouped together a media item can be almost any kind of content audio video multi media etc for example a song a book a newspaper or magazine article a movie a piece of a radio program etc media items might also be artists or albums if a mediaset is composed of a single type of media items it is called a homogeneous mediaset otherwise it is called a heterogeneous mediaset a mediaset can be ordered or unordered.