1. A non-transitory computer readable medium including program code for providing a message-based interface for requesting the creation of a retail allocation, 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 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 creating a retail allocation of merchandise between external suppliers and stores in the retail industry that includes a first message package derived from the common business object model and hierarchically organized in memory, the hierarchical organization of the first message package including: at a first hierarchical level within the first message package, a retail allocation create request message entity; and at the first hierarchical level within the first message package, a retail allocation package, where the retail allocation package includes, at a second hierarchical level within the first message package, a retail allocation entity and an item package, where the retail allocation entity includes, at a third hierarchical level within the first message package, a description, where the item package includes, at the third hierarchical level within the first message package, at least one item entity, and where each item entity includes, at a fourth hierarchical level within the first message package, a material internal ID; program code for processing the first message based on the hierarchical organization of the first message package, where processing the first message includes unpacking the first message package based on the first message package's structure and the first message package's derivation from the common business object model, wherein the particular structure of the first message package is used at least in part to identify the purpose of the first message; 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.