[rules-users] First Order Logic - METHODS in Drools

[Swindells, Thomas]

I thought wrapping a method in a eval statement is effectively allowing you to use methods directly, it is syntactic sugar to say this is a method call, evaluate it and then use the result in the rete graph.

>From what I understand the problem with methods is drools has to assume that the method always returns the same result given the same set of inputs and has no side effects as it is non-deterministic how many (or few) times the method is called and if the return value changes on different calls then it can really screw things up. When writing beans getters normally follow this rule by convention and necessity, however this is much less likely for arbitrary methods hence why it is good (IMHO) to force the user to consider what they are doing explicitly.

Thomas

> -----Original Message-----
> From: rules-users-bounces at lists.jboss.org [mailto:rules-users-
> bounces at lists.jboss.org] On Behalf Of Arjun Dhar
> Sent: 20 April 2011 05:29
> To: rules-users at lists.jboss.org
> Subject: [rules-users] First Order Logic - METHODS in Drools
>
> According to First order Logic, (from a rule perspective), one can
> represent
> their statements using:
> PREDICATES, METHODS, CONNECTORS (including existential quantifiers)
>
> ..while PREDICATES can be synonymous with Object and Object
> expressions; the
> only way of using methods  has been via "eval" (AFAIK, as per my
> outdated
> knowledge); and this is discouraged for the fact that evals perhaps
> dont fit
> in the RETE-OO scheme of things.
> Please note: By methods I dont bean Bean getter/setters; but work horse
> service layer methods.
>
> ..however, to be true to FOL, using methods directly should be
> supported.
> Q1) If it is, can one show or state an example?
> Q2) If not, for METHODS that return a specific type of Object, cant
> they be
> useful in RETE-OO evaluation?
> Q3) I've used "from" for DAO's , conceptually does "from" address this
> fully? In FOL (imo) PREDICATES & METHODS can be exchanged freely, not
> sure
> if "from" gives that freedom.
>
> thanks
>
>
>
>
> --
> View this message in context: http://drools.46999.n3.nabble.com/First-
> Order-Logic-METHODS-in-Drools-tp2841531p2841531.html
> Sent from the Drools: User forum mailing list archive at Nabble.com.
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users


**************************************************************************************
This message is confidential and intended only for the addressee. If you have received this message in error, please immediately notify the postmaster at nds.com and delete it from your system as well as any copies. The content of e-mails as well as traffic data may be monitored by NDS for employment and security purposes. To protect the environment please do not print this e-mail unless necessary.

NDS Limited. Registered Office: One London Road, Staines, Middlesex, TW18 4EX, United Kingdom. A company registered in England and Wales. Registered no. 3080780. VAT no. GB 603 8808 40-00
**************************************************************************************