decision trees

[RieksJ]

Work in progress on the new Sovrin guardianship paper has the following text (more or less), of which I wonder whether or not SGL could be a tool to actually help execute the generic decision-making algorithm identified at the bottom of this text.

In the Mya use-case, Malcolm immediately asks for a guardianship credential when Zo and Mya appear in his food tent. However, in general a visit from some arbitrary (set) of person(s) would go more like this:

A person in the shop says:

[I (the requester)] want to get a food ration for [someone].

The shopkeeper then executes the following algorithm:

Evaluate [someone] (i.e. replace it with an actual value);
IF (a ration has been dispensed for [someone] today)
THEN deny the request and stop.
ELSE	evaluate [I (the requester)];
IF ([someone] == [I (the requester)])
THEN dispense a ration for [someone] and stop.
IF (a [guardianship] exists, such that:
     ( [guardianship].dependent == [someone] AND
	  [guardianship].grant == “food” AND
	  [guardianship].guardian == 
	    (    [I (the requester)]
	    OR ( [party] 
		  AND a [mandate] exists, such that:
		    ( [mandate].mandator == [party] AND
			[mandate].mandatee == [I (the requester)]
			[mandate].grant == “food”
		    )
	       )
	    )
       )
    )
THEN dispense a ration for [someone] and stop.
IF (a [mandate] exists, such that
      ( [mandate].mandator == [someone] AND
	  [mandate].mandatee == [I (the requester)]
	  [mandate].grant == “food”
	 )
    )
THEN dispense a ration for [someone] and stop.
deny the request and stop.

As you may see, this algorithm could be made generic, with three arguments:

1. a condition that, when satisfied, immediately denies the request (e.g. 'a ration has been dispensed for [someone] today').
2. a permission (e.g. "food");
3. the action that is executed when the request is granted (e.g. 'dispense a ration for [someone]' - b.t.w., note that this dispensing implies logging (date(today), [someone]), so that it can be checked that a ration has been dispensed to [someone] on [date]).

Would it be useful to be able to express the following JSON? Would that be executable?

{
    "actionid": "dispense daily food ration",
    "postcondition": {
        "all": [
            { "a ration has been dispensed for [someone] today" },
            { "[logfile] += '{date(TODAY)}, {[someone]} has been provided a food ration')" },
        ]
    },
    "boundarycondition": {
        "[provider] has role:'shopkeeper'"
    },
    "precondition": { 
        "any": [
            { "[someone] == [requester]"
            },
            { "[someone] ==    [guardianship].[dependent] 
                            /\\ [guardianship].grant == 'food'
                            /\\ [guardianship].guardian == [requester] "
            },
            { "[someone] ==    [guardianship].[dependent] 
                            /\\ [guardianship].grant == 'food'
                            /\\ [guardianship].guardian == [party]
                                /\\ [mandate].mandator == [party]
                                /\\ [mandate].mandatee == [requester]
                                /\\ [mandate].grant == 'food'"
            },
            { "[someone] == [mandate].mandator
                            /\\ [mandate].mandatee == [requester]
                            /\\ [mandate].grant == 'food'"
            }
        ]
    }
}