Serializing a derived class

[deja]

hi,

I have a web service that builds an arraylist of objects. These objects
are derived classes of a base class with a few extra fields for help
with processing. But when I return the objects I only want to return
the base class implementation i.e

public class ServiceObject : BaseObject
{
public string helper1;
public string helper2;
public string helper3;
}

When the arraylist is returned, I want the client to see a bunch of
BaseObject objects NOT a bunch of ServiceObject objects. What is the
easiest way of doing this? I thought I could probably use some
serialization instructions but I'm not 100% sure on how to do it.

thanks
Phil