SOAP Web services: object aliasing in response?

Question

If a web service returns an object graph where some objects appear multiple times, will the data about these objects necessarily be duplicated in the transport format?

Put differently: With Java serialization, each object's state is written only once, and subsequent references to that object are mere pointers within the serialization stream. Is there a (preferable portable, i.e. WI-Basic-Profile compliant) way to achieve the same when (un)marshalling a webservice request or response?

Example: Given the classes

class Project {
    Task[] tasks;
}

class Task {
    User assignee;
}

class User {
    // some data
}

The webservice is supposed to return a Project, and I'd like to send each User at most once, regardless of how many tasks he is assigned in the project.

Answer 1

It appears that SOAP can serialize object graphs by using encodingStyle, but using encodingStyle contradicts WS-I Basic Profile 1.1. (source)