如何从wcf服务中检索未知类型？

I'm currently working on a wcf service that does some lookups in a database and return the data to the client. The user has entered an id of something he wants to see in a textbox. This could be a client-id, a product-id, an order-id or whatever. The lookup method on the server tries to find the id in the client table. If it's not in there it goes on the the product table etc, until it's found. I'm currently working on a wcf service that doe