When objects in memory are to be passed across a network to another host or persisted to storage, their in-memory representation must be converted to a suitable out-of-memory format. This process is called marshalling, and converting back to an in memory representation is called demarshalling.

In marshalling, several things must occur. Objects must be respresented with enough information that the destination host can understand the type of object being created. The objects’ state data must be converted to the appropriate format. Complex object trees that refer to each other via object references (or pointers) need to refer to each other via some form of ID that is independent of any memory model.

During demarshalling, the destination host must reverse all that and must also validate that the objects it receives are consistent with the expected object type (i.e. it validate that it doesn’t get a string where it expects a number).

In web services, objects are typically marshalled by converting them to an XML representation according to a standard such as SOAP. Objects can also be serialzed into a binary format, which in turn can be wrapped in a SOAP header. However, such formats run the risk of being too proprietary or platform specific to be useful for all potential clients.

See also: Object Serialization / Deserialization