1. A data structure stored on a hardware device comprising a multimedia content item that includes descriptive metadata about a content item and instructions for acquiring the multimedia content item, wherein the data structure is comprising a Media Description comprising: a package comprising one or more parts, wherein the one or more parts are described using an extensible markup language (XML), wherein at least one part has a content type, each content type comprising at least a media type and a subtype; at least a first relationship element identifying a relationship between the one or more parts in the package, wherein the relationship is described using the extensible markup language (XML); at least one connection between one or more parts in the package, wherein the connection is discovered by analyzing the relationship associated with the one or more parts in the package; at least a second relationship element identifying a source part; at least one attribute identifying a target part in each of the first and second relationships; at least one attribute identifying a name, wherein the name identifies a purpose of each of the first and second relationships; at least one selector part selecting between the one or more parts; at least one sequence part combining two or more parts into a single part; at least one package markup definition component; and rendering the Media Description.
3. The data structure of claim 1 , wherein the relationship element does not alter any parts in the package.