[rules-users] Guvnor Vs Mvel

Hi All, I am still evaluating the technology to use in the following use case: There is an input object and an output object. These objects are complex in the sense that they have collection of objects inside. Need to give a feature with which user can tell that when the input object contains certain values(this might be a complex expression) then set a value in certain field of output object. We need to build a UI and an ability to store the rules in db and apply them against the incoming objects. At first, I thought we can use Guvnor, but it is a lot more than what we need. We do not need a rule engine exactly, but a way to evaluate the expression. So I went to see using Mvel as a tool. Now I see the difficulty in converting the UI specific info to the Mvel expression. The expressions are becoming so complex. Is there any way I can say some thing like a drools rule which can be converted into a Mvel expression before evaluation? Let me know, if I need to be more clear.