1. A tangible computer readable medium including program code for providing a message-based interface for exchanging information regarding a declaration to a customs authority for exporting goods according to legal requirements, the medium comprising: program code for receiving via a message-based interface derived from a common business object model, where the common business object model includes business objects having relationships that enable derivation of message-based interfaces and message packages, the 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 a request for processing an export declaration that includes a first message package derived from the common business object model and hierarchically organized in memory as: an export declaration processing request message entity; and an export declaration package comprising an export declaration entity; program code for processing the first message according to the hierarchical organization of the first message package, where processing the first message includes unpacking the first message package based on the common business object model; and program code for sending a second message to the heterogeneous application responsive to the first message, where the second message includes a second message package derived from the common business object model to provide consistent semantics with the first message package.