1. A computer readable medium including program code for providing a message-based interface for a document output request, including a set of output requests related to a business document, the medium comprising: program code for receiving via a message-based interface exposing at least one service as defined in a service registry and from a heterogeneous application executing in an environment of computer systems providing message-based services, a first message for requesting output of a business document, including a set of output requests related to a referenced business object, the output requests using one or more output channels for sending out documents, the first message including a message package hierarchically organized as: a document output request message entity; a message header package including a message header entity; and a document output request package including a document output request entity, wherein the document output request entity includes an access control list entity, and wherein the document output request entity includes a universally unique identifier (UUID), a reference object node identifier (ID), a reference object type code, and a reference object node type code; and program code for sending a second message to the heterogeneous application responsive to the first message.