Hennesey,

Returning a DataSet is the least interoperable way of returning data to
non-.NET clients.  Why?  There's a lot of information that the DataSet
encapsulates that the client might not need.  Also, you suffer a
performance hit when you're trying to serialize/deserialize all that
metadata.

Have you thought about transfering a data contract or message contract?
By a data contract, I mean a user defined data type that can serialize
through SOAP so it can deserialized by any other client.  You can
create this data contract by either usign a code-frist (write the
object code) or contract-first (create the XML Schema first)
approaches.

In other words, take for example this sample customer data contract
(class) in C#:

public class Customer
{
 public string Id;
 public string Name;
}

If you use the classes & attributes under the System.Xml.Serialization
namespace, you can decorate your class like this:

[XmlRoot]
public class Customer
{
 [XmlElement]
 public int Id;

 [XmlElement]
 public string Name;
}

This will produce the following XML when the type is serialized:

<Customer>
 <Id>1234</Id>
 <Name>Test Customer</Name>
</Customer>

Since you're using this through an ASP.NET web service, you can let
ASP.NET do the dirty work and create the wsdl for you that will
encapsulate the XML Schema for your Customer data contract.  The XML
Schema for the Customer contract:

<xs:complexType name="Customer">
 <xs:sequence>
    <xs:element minOccurs="1" maxOccurs="1" name="Id" type="s:int" />
    <xs:element minOccurs="0" maxOccurs="1" name="Name"
type="s:string" />
 </xs:sequence>
</xs:complexType>

interpretation of the Customer data contract using specific Java data
types.  For example, your generated Customer Java class from the above
schema will look like:

/**
* Generated Customer class
*/
public class Customer {

   private int idField;

   private String nameField;

   public int get_Id() {
       return this.idField;
   }

   public void set_Id(int value) {
       this.idField = value;
   }

   public String get_Name() {
       return this.nameField;
   }

   public void set_Name(String value) {
       this.nameField = value;
   }
}

As you can see, you can now exchange "complex" data types between your
.NET Web service and Java client.  Remember, you're exchanging
contracts (schemas) not types (classes).

Hope this helps you out!

- Javier