Loop through attributes in form
     If attribute checked
          select * from ProductAttributes where attributeId = attributeselected
          If EOF
             insert into ProductAttributes...
          End If
     Else
         select * from ProductAttributes
         Loop until EOF
             If checked in ProductAttributes table
                  Delete row
             End If
         End Loop
     End If
End Loop

select AttributeId, Checked="Y" from ProductAttribute where ProductId = @ProductID
union all    -- product specific
select AttributeId, Checked="N" from Attribute where AttributeId not in (select AttributeId, Checked="Y" from ProductAttribute where ProductId = @ProductID)
--
-- this will give you a result set, of a full set of possible Attributes for the given Product, with Checked = {Y|N}, which you will load into memory (object, DataWindow, whatever)
-- display the set (“form” that allows changes to Attribute for a Product)
-- allow the user Un/Check the box/column of the set/form in memory
-- track the changes to columns in memory (if FieldChanged ...)
-- upon SaveClicked, for each changed row in the set/form in memory:
--     if Checked then insert ProductAttribute ... 
--     if Unchecked then delete ProductAttribute ...