8. A key task for any team pursuing a PFI deal is translating the Customer's requirement (normally expressed in a User Requirement Document (URD) containing Key User Requirements (KURs)) into an output based specification (OBS) document. The OBS must clearly describe the service outputs and performance standards required to be met by the contractor, together with any regulatory, security or other constraints within which the service has to be delivered. The payment and performance mechanism will link directly to the OBS ensuring that the contractor is appropriately incentivised to deliver the required output. It is therefore important for both these elements of the deal to be developed in tandem.