Although there may be many kinds of instruments, the main one described here is the Compute instrument, which corresponds to a processor or set of processors along with associated memory, temp files, software, etc. If the same variable name is used in multiple places, it has the effect of constraining those values to be the same. Additional constraints on the variables are provided in a separate constraint list. I understand they might be gone if I confirm, but I also expect them to be cheaper than Pending resources. This has the dual purpose of identifying the user for billing purposes, and determining the resources that this user is authorized to use.
Maximum user is willing to pay for use of object.
Null on the first call for a particular negotiation, and after that, the value returned from the previous order-window transaction for this negotiation. It simply allows the AO to follow a single negotiation through several interactions. In the end, this serves as an authorization to pick up the resource object at the Pickup Window. If the negotiation ID passed to the AO was a valid non-null value, this is the same value. No negotiation ID is returned for Stats or Cancel requests.