[rules-dev] Backwards chaining: the difference between input and output variables
Wolfgang Laun
wolfgang.laun at gmail.com
Thu Apr 21 02:27:48 EDT 2011
Designing syntax well is not easy. With extensions, one should strive for as
much
conformity with the existing language, while trying to follow general
principles.
One might have discussed (for instance) the use of field names for
referencing
the query relations, taken from their parameter definition. And then one
could write,
as usual:
?editableThings(food: thing, location == loc )
or
?editableThings(food: thing, loc: location )
And the in/out is clear to all who know a little legacy DRL.
And the ugly semicolon evaporates.
And the maintainability/readability disadvantage of "positional" is gone.
Cheers
-W
On 20 April 2011 22:52, Michael Anstis <michael.anstis at gmail.com> wrote:
>
> Simple yes, but consistent too should be a factor.
>
> Most questions we have to the user mailing list involve people writing DRL
not using tooling.
>
> So DRL, IMO, has to be seen as the "tool" to author rules. Drop the
proposed colon altogether or make it's use consistent.
>
> On 20 April 2011 17:42, Mark Proctor <mproctor at codehaus.org> wrote:
>>
>> My personally opinion is to keep the language simple and instead have the
tooling inject what ever is necessary as a visulation. Be it different
colouring, hover over or graphic symbol. It keeps the language simple and
actually achieve the desired result better.
>>
>> Mark
>> On 20/04/2011 14:00, Leonardo Gomes wrote:
>>
>> +1 for Michael's suggestion.
>>
>> It's a bit more verbose, but makes things clear.
>>
>> The semicolon here:
>> ?editableThings(food : ?, loc;)
>>
>> Is a typo, right? You actually meant:
>>
>> ?editableThings(food : ?, loc);
>>
>> - Leo.
>>
>>
>>
>> On Wed, Apr 20, 2011 at 11:59 AM, Michael Anstis <
michael.anstis at gmail.com> wrote:
>>>
>>> Hmmmmm....
>>>
>>> Personally, I don't like the use of ":" i isolation as it's what we
currently use to bind variables and I feel "cheese:" as an output definition
could just make people question whether they've missed something. Perhaps
"cheese : ?" would be a viable alternative. This would be in keeping with
(a) current variable declaration, (b) the use of "?" to identify a call to a
query. Geoffrey's examples would then become:-
>>>
>>> rule outputinput
>>> when
>>> Here( loc : location)
>>> ?editableThings(food : ?, loc;)
>>> then
>>> System.out.println("Food " + food + " at location " + loc);
>>> // Output:
>>> // Food crackers at location kitchen
>>> // Food apple at location kitchen
>>> end
>>>
>>> rule outputOutput
>>> when
>>> ?editableThings(food : ?, loc : ?;)
>>> then
>>> System.out.println("Food " + food + " at location " + loc);
>>> // Output:
>>> // Food crackers at location kitchen
>>> // Food apple at location kitchen
>>> // Food chocolate at location living room
>>> // Food chips at location living room
>>> end
>>>
>>> rule typo
>>> when
>>> Here( looc : location)
>>> ?editableThings(food : ?, loc : ?;)
>>> then
>>> System.out.println("Food " + food + " at location " + loc);
>>> // Output:
>>> // Food crackers at location kitchen
>>> // Food apple at location kitchen
>>> // Food chocolate at location living room
>>> // Food chips at location living room
>>> // looc is just an unused bound variable
>>> end
>>>
>>> On 20 April 2011 10:16, Geoffrey De Smet <ge0ffrey.spam at gmail.com>
wrote:
>>>>
>>>> Mark and I were discussing backwards chaining
>>>>
http://blog.athico.com/2011/04/backward-chaining-emerges-in-drools.html
>>>> on IRC and we 'd like your opinion on a design issue.
>>>>
>>>> The example
>>>> ========
>>>>
>>>> Let's say you have this data:
>>>> Location("crackers", "kitchen")
>>>> Location("apple", "kitchen")
>>>> Location("chocolate", "living room")
>>>> Location("chips", "living room")
>>>>
>>>> Let's say you have this code:
>>>>
>>>> query editableThings( String thing, String location )
>>>> Location(thing, location)
>>>> end
>>>> And then these 3 rules:
>>>>
>>>> rule outputinput
>>>> when
>>>> Here( loc : location)
>>>> ?editableThings(food, loc;)
>>>> then
>>>> System.out.println("Food " + f + " at location " + loc);
>>>> // Output:
>>>> // Food crackers at location kitchen
>>>> // Food apple at location kitchen
>>>> end
>>>>
>>>> rule outputOutput
>>>> when
>>>> ?editableThings(food, loc;)
>>>> then
>>>> System.out.println("Food " + f + " at location " + loc);
>>>> // Output:
>>>> // Food crackers at location kitchen
>>>> // Food apple at location kitchen
>>>> // Food chocolate at location living room
>>>> // Food chips at location living room
>>>> end
>>>>
>>>> rule typo
>>>> when
>>>> Here( looc : location)
>>>> ?editableThings(food, loc;)
>>>> then
>>>> System.out.println("Food " + f + " at location " + loc);
>>>> // Output:
>>>> // Food crackers at location kitchen
>>>> // Food apple at location kitchen
>>>> // Food chocolate at location living room
>>>> // Food chips at location living room
>>>> end
>>>>
>>>> The discussion
>>>> =========
>>>>
>>>> Both rules have the same statement:
>>>> ?editableThings(food, loc;)
>>>>
>>>> In the outputInput rule, "loc" is an input variable.
>>>> In the outputOutput rule, "loc" is an output variable.
>>>>
>>>> I am wondering if we don't need a visual demarcation that a variable is
an output variable,
>>>> to make it stand out of an input variable?
>>>>
>>>> Proposition 1: Suffix output variables with ":"
>>>>
>>>> rule outputinput
>>>> when
>>>> Here( loc : location)
>>>> ?editableThings(food:, loc;)
>>>> then ... end
>>>>
>>>> rule outputOutput
>>>> when
>>>> ?editableThings(food:, loc:;)
>>>> then ... end
>>>> rule typo
>>>> when
>>>> Here( looc : location)
>>>> ?editableThings(food:, loc;) // compiler error because input
variable loc is not declared
>>>> then ... end
>>>>
>>>> --
>>>> With kind regards,
>>>> Geoffrey De Smet
>>>> _______________________________________________
>>>> rules-dev mailing list
>>>> rules-dev at lists.jboss.org
>>>> https://lists.jboss.org/mailman/listinfo/rules-dev
>>>>
>>>
>>>
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>>
>>
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