Using a message exchanger ("message exchanger"), data messages are exchanged between entities in a decentralized, distributed, potentially heterogeneous, network environment. The message exchanger employs XML (extensible Markup Language). To accomplish this, the entities on both ends of the message exchange understand, identify, and parse the message format. The message exchanger defines such a mechanism. Data messages are broken down into two portions--one portion (the body) is intended from an ultimate destination and the other portion (the header) is intended for intermediate destination and/or the ultimate destination. The body may be defined so that it must be understood by the ultimate destination. The header may be defined so that it must be understood or changed. Regardless, the data in the body is delivered intact to the ultimate destination. The message exchanger defines a message envelope exchange format in XML over a transport protocol, such as HTTP (HyperText Transport Protocol). This format allows for the execution of RPC (Remote Procedure Call) over XML, but it can be used for any message exchange over a network.