Feature request - Decision Tables

[arsalans]

@CacheControl I was wondering if this rule engine can support decision tables.

What do I mean by that:
So a decision table is composed of many rules that differ usually by one or more conditions. So, for example, I will create a decision table to implement this logic:

Colour - Price
Blue - 10
Red - 11
Green - 13
Yellow - 14
Pink - 8
White - 13
Black - 20

So, you will read it like this, if a color is "Blue" then the price is $10. So instead of creating 7 separate rules, I will only create one rule, a decision table rule. Let me know what do you think.

[CacheControl]

@arsalans interesting concept. My understanding of decision trees is that for each permutation of the conditions, there is a defined set of actions. Although it would be easy for the engine to take in a list of conditions and compute a rule per permutation, I'm confused as to how the engine would know the appropriate event to fire in each circumstance. Maybe I just need you to expand on the use case you provided so I can understand the problem you're trying to solve.

[arsalans]

@CacheControl So, how about if I write my rule like this, and again, I am trying to be as naive as possible:

var decisionTable = 
{
	{
		"color": "Blue",
		"price": 10
	},
	{
		"color": "Red",
		"price": 11
	},
	{
		"color": "Green",
		"price": 13
	},
	{
		"color": "Yellow",
		"price": 14
	}
};

var helper =
{
	"condition": "color",
	"event": "price"
};

new DecisionTable (decisionTable, helper);

So now, the DecisionTable object knows what are the conditions and what are the events to send.

[CacheControl]

@arsalans Ah ok, I think I get it now. In json-rules-engine vernacular it's essentially wanting to vary the event based on which condition succeeded.

To me, this almost feels like an accessory package that would act as a rule generator - it would take in the decision tree data structure you posted above, and use it to generate a rule per decisionTable row. json-rules-engine would be responsible for the lower-level execution of the generated rules.

Alternatively, you may want to look at the ruleResult feature just released in 2.0.0 - you can use the ruleResult argument provided in the success/failure events to determine which condition was successful, and use the condition's factResult("yellow", "red", etc) to lookup from a prices hash you maintain outside the engine.

It terms of whether or not this belongs in json-rules-engine itself, right now it feels like something I'd like to keep separate; I want to keep json-rules-engine as the low level executor of basic boolean logic + firing events, while more complex rule orchestrations such as decisionTables are probably better suited as plugins/extensions.

[CacheControl]

Here's the ruleResult docs I mentioned above.