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Re: [PRD] ACTION-531 Update PRD examples complete

From: Christian de Sainte Marie <csma@ilog.fr>
Date: Fri, 20 Jun 2008 10:24:25 +0200
Message-ID: <485B6939.80402@ilog.fr>
To: Gary Hallmark <gary.hallmark@oracle.com>
CC: RIF WG <public-rif-wg@w3.org>

Gary, all,

Sorry if it sounds like I am backtracking on something I agreed to, but, 
after having a look at the examples in the new presentation syntax, I 
realized that I cannot live with that.

Long, detailled, substantiated explanations follow, but, to make a long 
story short, I propose that:
- either we revert to a more production rules friendly PS;
- or we restrict the use of the PS for what if was initailly designed, 
that is, make the semantics easier to specify and read, and that we use 
some informal pseudo-code for the presentation of the running example in 
the introduction. E.g.:

  IF ?c is a chicken such that the age of ?c in months is > 8
     AND ?p is a potato such that ?p is owned by ?c;
              AND the weight in decigrams of ?p > (age of ?c)/2;
     AND today is not Tuesday
     AND there is no fox in the hen house
  THEN mash ?p
       AND increase the grain allowance of ?c by 10%
       AND remove the couple (?c, ?p) from the ownership relation.

The current PS for the running example just looks too weird: a 
significant share of PRD's target will not be able to relate to it, even 
to the point of not being able to understand what it means without quite 
some effort and rewriting work, esp. among that part of the crowd that 
is most important wrt adoption, that is, the commercial developpers 
(application developpers and rule engines/management system vendors).

Gary, honestly, what would be the reaction of the developers in your 
team if you showed them the example without some serious background 
explanation (and even with)?

As I said and wrote again and again, I do not buy into the argument that 
PRD's PS must make the overlap with BLD more obvious. The main reason is 
because that argument is completely irrelevant:
1. The primary target for PRD will not be familiar with BLD, at least 
not when they will read PRD (because they are more likely to read PRD 
first), so, they will see no similarity anyway;
2. The people who will be interested in the overlap will either read the 
comparison in the appendix, and read BLD with that in mind, or, if they 
are familiar with BLD already, they are likely to look at the appendix 
first, when they look at PRD;
3. The people who want to write PRD-compatible BLD rules will write them 
in their prefered BLD syntax, rather than some weird 
BLD-like-but-not-quite PRD PS, anyway;
4. The nice thing about sharing a common XML serialisation for the 
intersection between BLD and PRD is precisely that one does not have to 
care which kind of language and syntax a rule has been initially written 
  in (BLD-ish or PRD-ish): if you can parse it, you can use it, whether 
you parse it in BLD or PRD. The beauty of it and the appeal of it *is* 
the transparency.

Again, I believe that the first example must tell the PR people that, 
yes, this is the kind of familiar looking rule that PRD is about; and, 
yes, this is what PRD serialize, including those parts of the condition 
that are attached to the declaration of variable and that Gary dislikes 
so much: they are so currently used that many people believe that the 
clauses in the condition of a PR are ordered, and, if people write their 
rules that way, PRD must preserve the investment they made in deciding 
the scopes for the variables (and our running example must tell them 
that it is the case). That is why I insist that we keep the "such that" 
parts in the example rule as well.

To make sure that it was not just me, I did some research and gathered 
some evidence that the overwhelming usage in the PR crowd is IF 
condition THEN action. See below.


First, I did a quick poll amongst the developers in the JRules team at 
ILOG. I wrote:

A :- B

on a piece of paper, and I shown it to the first 10 people I met from 
the team, asking what it was. The result is striking:
- 6 did not know (3 guessed that it might be a assignement in some weird 
programming language; after I told them that it was a rule, 4 still did 
not know what to make out of it, and 2 read it A implies B, one of which 
1 said she had had some training in Prolog at the University)
- the remaining 4, who recognised that it was a rule, said: A implies B.

I also googled the Web for evidence. And I only found more evidence that 
everybody in the PR world wrote their rules, and thought of rules, with 
the condition part first and the conclusion/action part next:

- First example of a rule in the documentation of Drools (JBoss Rules) [1]

	rule "Primitive int manual unbox"
	    $c : Cheese( $price : price )
	    $c.setPrice( $price.intValue() * 2 )


- Jess documentation [2] about rules:

"Rules are defined in Jess using the defrule construct. A very simple 
rule looks like this:

Jess> (defrule welcome-toddlers
     "Give a special greeting to young children"
     (person {age < 3})
     (printout t "Hello, little one!" crlf))

This rule has two parts, separated by the "=>" symbol (which you can 
read as "then".) The first part consists of the LHS pattern (person {age 
< 3}). The second part consists of the RHS action, the call to println. 
If you're new to Jess, it can be hard to tell the difference due to the 
LISP-like syntax, but the LHS of a rule consists of patterns which are 
used to match facts in the working memory, while the RHS contains 
function calls."

[2] http://herzberg.ca.sandia.gov/docs/70/rules.html

- First example of a rule in CLIPS documentation [11]:
"The pseudocode for a rule about duck sounds might be

  IF the animal is a duck
  THEN the sound made is quack"

(and the rule is:
defrule duck "Here comes the quack"      ; Rule header

    (animal-is duck)                      ; Pattern

=>                                       ; THEN arrow

    (assert (sound-is quack)))            ; Action

[11] http://clipsrules.sourceforge.net/documentation/v630/ug.htm

- First example in Oracle rule language I found [3]

rule approvePO
  if (fact PurchaseOrder po
      && po.amount > 1000
      && po.approvalLevel == null)
   po.approvalLevel = "VP";


- Basic operation of a production system, according to Wikipedia [4] 
(notice the refence to LHS and RHS without an explanation, as if it was 
"Rule interpreters generally execute a forward chaining algorithm for 
selecting productions to execute to meet current goals, which can 
include updating the system's data or beliefs. The condition portion of 
each rule (left-hand side or LHS) is tested against the current state of 
the working memory.

In idealized or data-oriented production systems, there is an assumption 
that any triggered conditions should be executed: the consequent actions 
(right-hand side or RHS) will update the agent's knowledge, removing or 
adding data to the working memory. The system stops processing either 
when the user interrupts the forward chaining loop; when a given number 
of cycles has been performed; when a "halt" RHS is executed, or when no 
rules have true LHSs."

[4] http://en.wikipedia.org/wiki/Production_system

- Pega does not provide an example in their front page about rule 
technology, but it mentions "if-then" rules [5]. Same for Fair Isaac [6] 
(I do not have access to either Pega nor Blaze documentation).

[5] http://www.pega.com/Products/RulesTechnology.asp

- IBM on business rules: "Business rules can be thought of as an if-then 
business decision". (Googling "IBM production rule" points towards 
CommonRule, which is not alive anymore at IBM, as far as I know (IBM 
folk?), so I tried again with "IBM business rule").


- The first example of a rule on the RuleML home page [8] is a 
production rule:
"If you want to review rule principles, (then) you may look at 
Rule-Based Expert Systems. (BTW, this is itself a simple rule.)"

[8] http://www.ruleml.org/

- And the first example in the presentation to wich 'Rule-Based Expert 
Systems' links [9] is another production rule:
"IF the engine is getting gas AND the engine will turn over THEN the 
problem is spak-plugs"

[9] http://www.cs.nott.ac.uk/~sxp/ES3/sld003.htm

- The first example rules in REWERSE is not a production rule, but their 
visualisation tools still produces an if-then form [10]:
"Rule Text: If X is the parent of Y and X is brother of Z then Z is the 
uncle of Y"

[10] http://oxygen.informatik.tu-cottbus.de/visualization/v1/

- First definition and example of a rule in Haley's RuleBurst 
documentation [12]:

"A rule is an if-then statement."

;if a then b
;or, in other words, a implies b
;or, in Eclipse,
(defrule a_implies_b
(assert (b))

Received on Friday, 20 June 2008 08:24:38 UTC

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