<asp:ObjectDataSource runat="server"  TypeName="Data.Bar`1[[Data.Foo]]"   SelectMethod="GetData"/>

using System;
using System.Data;

namespace Data
{
    public class Foo{}

    public class Bar<T>
    {
        public DataSet GetData()
        {
            throw new NotImplementedException();
        }

        public DataSet GetData(int ID)
        {
            throw new NotImplementedException();
        }
    } 
}