3 tier using WCF in .Net

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VB

hi,

I have developed a 3 tier application in vb.net 2008 which has User Interface Layer, Business Layer and Data Access Layer.

Now I want to distribute the application in online. I have decided to host the service using WCF.

I have read more articles in the net about WCF. I have learned In WCF single Service Class can host. But we can use multiple interface and multiple data contracts.

But in my application I can't decide how to create service host for my application.

I explain my senerio.
The client application contains UI and BL - in client machine
The WCF service application caontains DL - in server machine
BL and DL communicate via WCF

UI contains more forms ( more than 50) each one have different data contracts

but all forms have some common functions to communicate to DL

so I have decided to define my service contract as common for all forms as below

<servicecontract()> _
 Public Interface SetupMasterFrmServiceContract

      <operationcontract()> _
      Sub DataNew()

      <operationcontract()> _
      Function DataProcess(ByVal xdata As Combositetype,ByVal xMode As Char) As Boolean

      <operationcontract()> _
      Sub DataOpen(ByVal x As String)

      <operationcontract()> _
      Sub DataFetch()

  End Interface

but in the above code in the line

Function DataProcess(<b>ByVal xdata As Combositetype</b>,ByVal xMode As Char) As Boolean

the combositetype is vary for every form. how can I define the service contract for all forms. If I declare interface for every form then it is very vauge to implement the service class.
Please explain how to declare and define my service contract.