[rules-users] Web decision tables (Guvnor)

[Vincent LEGENDRE]

Hi 

I was wondering why you need the otherwise here. 
May be it is only because you have simplified your sample, but the table you sent is like a truth-table telling what currency can be converted for a particular account. 
So, as you have a 2 state answer, you can simply add rules to specify the "true" answer, by modifying the answer flag that is set to false initially. In other words, you cannot convert the currency unless a rule have triggered to set the flag to true. Or if you use a fact to store the answer, if the fact is there you can convert, if not (because no rule had triggered) you can't convert. 

This way, your table becomes quite simple, but I don't know if my assumption is generalizable to your whole application. 

----- Original Message -----

From: "Michael Anstis" <michael.anstis at gmail.com> 
To: "Rules Users List" <rules-users at lists.jboss.org> 
Sent: Friday, August 10, 2012 5:07:54 PM 
Subject: Re: [rules-users] Web decision tables (Guvnor) 

Hi Stephen, 

You've made my afternoon ;) 

The operation of "otherwise" is rather dumb. It does not have any understanding of what groups of rows it is meant to limit it's search of values to construct the "not in...." part. 

As you have discovered, in your case, the Account column has no significance at all (to the web-guided decision table) although it does to the business analyst. 

The immediate workaround would be to move each "group" to a different decision table; i.e. Account=1 and Account=2. I appreciate your example is probably a simplification of the real problem. 

A better solution would be to furnish the "otherwise" value with the information it would need to determine it's search range. e.g. define "otherwise" with a key column of "Account". This is however an enhancement :( 

Feel free to raise a JIRA (for GUVNOR)... no promises as to when I'll get a chance to do anything about it though :( 

More complex requirements exist, for example given:- 


Account Qualifier Currency CanTrade 
1 A EUR Y 
1 A USD Y 
1 B IDR Y 
1 A Otherwise N 
2 A EUR Y 
2 B USD Y 
2 B Otherwise N 
Account=1, Qualifier=A, Otherwise = not in ("EUR", "USD") 
Account=1, Qualifier=B, There is no otherwise 
Account=2, Qualifier=A, There is no otherwise 
Account=2, Qualifier=B, Otherwise = not in ("USD") etc 

So "Otherwise" will need a set of key\group columns. 

With kind regards, 

Mike 

On 10 August 2012 15:50, Stephen Masters < stephen.masters at me.com > wrote: 




Hi folks, 


Given a decision table a bit like this (hopefully the monospaced font lays it out ok!): 


Account Currency CanTrade 
1 EUR Y 
1 USD Y 
1 IDR Y 
1 Otherwise N 
2 EUR Y 
2 USD Y 
2 Otherwise N 


LHS conditions are generated a bit like this: 
account == 1, currency == 'EUR' 
account == 1, currency == 'USD' 
account == 1, currency == 'IDR' 
account == 1, currency not in ('EUR', 'USD', 'IDR') 
account == 2, currency == 'EUR' 
account == 2, currency == 'USD' 
account == 2, currency not in ('EUR', 'USD', 'IDR') 


… which has the effect that for account 2, currency IDR, the rule does not fire. For the business analysts building the rules, this does't make a lot of sense, as they're expecting it to mean: 
account == 2, currency not in ('EUR', 'USD') 


Unfortunately this means that if a currency is permitted for one account, then a row must be added for every other account, indicating that the currency is not permitted. 


I'm trying to achieve a sensible default (fire the rule to reject the trade) unless the currency is explicitly permitted. 


Is there a decent mechanism for achieving this in a decision table? 


One alternative I can think of is to create a technical rule which logically inserts a rejection which exists as long as this rule hash't fired. But I would really prefer to avoid doing anything like that, as I reckon it would be something of a maintenance nightmare. 


Any thoughts? 


Cheers, 


Steve 


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