JESS: Backward-Chaining problem

[Joaquin Cañadas]

Hello,
I need help for this example that I have made with backward-chaining.
We use a template named Parral with 3 slots:
(deftemplate Parral
(slot Estado_Fenologico)
(slot Numero_Brotes)
(slot Dias_Hasta_Recoleccion))
We have a rule named Arana_Madurez that uses two slots 
Estado_Fenologico and Dias_Hasta_Recoleccion of the Parral fact.

(defrule Arana_Madurez
(Parral (Estado_Fenologico ?e)
(Dias_Hasta_Recoleccion ?d))
(test (eq (str-compare "N" ?e) 0))
(test (< (integerp ?d) 21))
=>
(printout t "HOLA" crlf)
(assert (Estado_Cultivo (Estado_Planta "MADUREZ")))
)
Using backward-chaining we ask the user for these values, in the rules 
create-Estado_Fenologico and create-Dias_Hasta_Recoleccion.

(defrule create-Estado_Fenologico
(need-Parral (Estado_Fenologico ?))
=>
(printout t "Estado Fenologico: ")
(assert (Parral (Estado_Fenologico (upcase (read)))))
)
(defrule create-Dias_Hasta_Recoleccion
(need-Parral (Dias_Hasta_Recoleccion ?))
=>
(printout t "Dias hasta recoleccion: ")
(assert (Parral (Dias_Hasta_Recoleccion (read))))
)
However, I have an error in the Arana_Madurez rule because when the 
create-Estado_Fenologico asserts the Parral fact, this fact only 
stores the value of Estado_Fenologico slot. The fact Parral exists 
now, and the Arana_Madurez rule is evaluated, producing an error 
because the Dias_Hasta_Recoleccion remains with a nil value and it 
isn4t a numeric value. Instead of evaluating the rule, the 
backward-chaining might fire the rule which ask for the 
Dias_Hasta_Recoleccion value.

The general idea is how to ask to the users the unknown slots which 
appear in the LHS rules, using backward-chaining. And how to assert the 
slots values of a fact in a independent way.

Thanks for any help.
The complete example is as follows:
; DEFINICION DE PLANTILLAS
;; ************************
(deftemplate Parral
(slot Estado_Fenologico)
(slot Numero_Brotes)
(slot Dias_Hasta_Recoleccion))
(deftemplate Estado_Cultivo
(slot Estado_Planta))
;; DEFINICION DE REGLAS
;; ********************
(do-backward-chaining Parral )
(defrule create-Estado_Fenologico
(need-Parral (Estado_Fenologico ?))
=>
(printout t "Estado Fenologico: ")
(assert (Parral (Estado_Fenologico (upcase (read)))))
)
(defrule create-Dias_Hasta_Recoleccion
(need-Parral (Dias_Hasta_Recoleccion ?))
=>
(printout t "Dias hasta recoleccion: ")
(assert (Parral (Dias_Hasta_Recoleccion (read))))
)
(defrule create-Numero_Brotes
(need-Parral (Numero_Brotes ?))
=>
(printout t "Numero de brotes: ")
(assert (Parral (Numero_Brotes (read))))
)
(defrule Arana_Madurez
(Parral (Estado_Fenologico ?e)
(Dias_Hasta_Recoleccion ?d))
(test (eq (str-compare "N" ?e) 0))
(test (< (integerp ?d) 21))
=>
(printout t "HOLA" crlf)
(assert (Estado_Cultivo (Estado_Planta "MADUREZ")))
)
(defrule Arana_Vigilar
(Parral (Estado_Fenologico ?e))
(test (eq (str-compare ?e "A") 0))
=>
(assert (Estado_Cultivo (Estado_Planta "VIGILAR")))
)
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