[rules-dev] salience alternative with before/after

[Greg Barton]

I think it would be a great idea as long as it's not just generating the salience code below under the covers. (Taking your example literally.)  But I assume you're just creating a conflict resolution relation based on the annotations.  This solves the main problem with salience which is it's global reach. (i.e. all rules marked with salience are related whether you want them to be or not.)  

Maybe more specifically worded annotations would be good: @firesBefore() and @firesAfter()

And you don't have it in the examples below, but I'm assuming you could have multiple before and after annotations per rule.

Also, you mentioned agenda-groups: could this be extended to those as well?  i.e. instead of groups activating in LIFO order, be explicitly ordered by annotation?

--- On Mon, 2/13/12, Mark Proctor <mproctor at codehaus.org> wrote:

> From: Mark Proctor <mproctor at codehaus.org>
> Subject: [rules-dev] salience alternative with before/after
> To: rules-dev at lists.jboss.org
> Date: Monday, February 13, 2012, 6:25 PM
> Davide has suggested a good idea.
> 
> Now that rules support annotations, and annotations with
> values. We 
> should add a before/after keyword to each rule.
> before/after would then 
> take a list of annotations. The idea is to use this to
> generate salience 
> under the covers.
> 
> rule resetBalance before( @cashflow ) when then end
> 
> rule debit @cashflow when then end
> 
> rule credit @cashflow when  then end
> 
> rule printBalance after(@cashflow ) when then end.
> 
> Salience gives one rule priority over another, thus it's
> declaring an 
> implicit relationship between rules. Yet it's a magic
> number that 
> doesn't easily show this relation, and as the rulebase
> grows it can be 
> very hard to determine those relationships as specified by
> salience from 
> reading the rules. before/after allows you to specify
> declarative the 
> relationships betwen rules in a more maintainable and
> readable way, even 
> if under the covers it's just generating:
> 
> rule resetBalance salience 100 when then end
> 
> rule debit salience 0  when then end
> 
> rule credit salience 0 when  then end
> 
> rule printBalance saliance -100 when then end.
> 
> Yes there are agenda-groups and ruleflow-groups, but they
> can be a bit 
> cumbersome compared to the simplicity of using salience.
> This way we get 
> the simplicity of using salience, without the downfalls of
> it being a 
> magic number.
> 
> What do people think? Any ideas on how we can improve this?
> At build 
> time it would have to report impossible to resolve
> relationships and barf.
> 
> Mark
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