[rules-dev] Perhaps an undocumented feature of Backward Chaining?

[Mark Proctor]

On 24/06/2011 21:22, Michael Anstis wrote:
> Your test, Mark, is not the same example to which Wolfgang refers.
>
> You'll need to re-test with the DRL at the end of Wolfgang's email 
> (which is what we've included in N&N for 5.2).
>
> It's quite possible one of the ?'s is simply wrong... but I don't 
> understand the subtleties of BC syntax yet.
If the query has "?" in it, then it's pull only. In which case the 
insertion order matters, as the query is triggered when Here or in below 
Person is triggered. Inserting the Location objects after the query is 
triggered will not return a result, unless you use leave off the "?" for 
a reactive "open query"

Mark
>
> With kind regards,
>
> Mike
>
> On 24 June 2011 21:14, Mark Proctor <mproctor at codehaus.org 
> <mailto:mproctor at codehaus.org>> wrote:
>
>     On 23/06/2011 13:20, Wolfgang Laun wrote:
>>     Still not resolved...
>>
>     I have added a test for all the possible insertion orders for that
>     particular use case and was not able to reproduce a problem:
>     https://github.com/droolsjbpm/drools/commit/501f2196dcef754eed5a28b066b50665a5bc29a3
>
>     MArk
>>     On 22 June 2011 21:40, Mark Proctor <mproctor at codehaus.org
>>     <mailto:mproctor at codehaus.org>> wrote:
>>
>>         heh, I made a mistake with the rule
>>         ( Location(z, y;) and ?hasFood(x, z;) )
>>         should be
>>         ( Location(z, y;) and hasFood(x, z;) )
>>
>>         Otherwise it's not reactive, and then ordering matters.
>>
>>         With that change I can do the insertions in any order and all
>>         is fine.
>>
>>
>>     This works for the example you gave. But the one taken from the
>>     "Introduction" still depends on the order the facts are inserted.
>>     Below is the .drl, which does not need any pojos. Rule kickOff
>>     contains the order that produces nothing to see and eat:
>>     You are in the table
>>       You can see []
>>       You can eat []
>>
>>     Insert Here after the others, and it works.
>>
>>     -W
>>
>>      import java.util.List
>>
>>     declare Thing
>>         thing : String @key
>>     end
>>
>>     declare Edible extends Thing
>>     end
>>
>>     declare Location extends Thing
>>         location : String  @key
>>     end
>>
>>     declare Here
>>         place : String
>>     end
>>
>>     rule kickOff
>>     when
>>     then
>>         System.out.println( "insert Here" );
>>         insert( new Here( "table" ) );
>>         System.out.println( "insert Edible" );
>>         insert( new Edible( "peach" ) );
>>         System.out.println( "insert Location" );
>>         insert( new Location( "peach", "table" ) );
>>     end
>>
>>     # 2011-06-22
>>     query isContainedIn( String x, String y )
>>         Location(x, y;)
>>         or
>>         ( Location(z, y;) and /*?*/isContainedIn(x, z;) )
>>     end
>>
>>     query whereFood( String x, String y )
>>         ( Location(x, y;) and
>>         Edible(x;) )
>>         or
>>         ( Location(z, y;) and /*?*/whereFood(x, z;) )
>>     end
>>
>>     query look(String place, List things, List food)
>>         Here(place;)
>>         things := List() from accumulate( Location(thing, place;),
>>                                           collectList( thing ) )
>>         food := List() from accumulate( /*?*/whereFood(thing, place;),
>>                                         collectList( thing ) )
>>     end
>>
>>     rule reactiveLook
>>     when
>>         Here( $place : place)
>>         /*?*/look($place, $things; $food := food)
>>     then
>>         System.out.println( "You are in the " + $place);
>>         System.out.println( "  You can see " + $things );
>>         System.out.println( "  You can eat " + $food );
>>     end
>>
>>
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>
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