1. A non-transitory, tangible computer readable medium including program code for providing a message-based interface for exchanging product-related information between a buyer and a vendor for planning purposes, 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 communicating information associated with at least one product-related activity of the buyer for use in performing supply planning for the buyer that includes a first message package derived from the common business object model and hierarchically organized in memory as: a product activity message entity; and a product activity package comprising a product activity entity and an item package, where the item package includes a product activity item and a product information package, and further where the product information package includes a product 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.