I am new to Drools. As per my usecase, I want to dynamically create the rules. I have considered using the following rule template:
template header
rule
eventType
package org.ossandme;
global org.ossandme.AlertDecision alertDecision;
template "alert"
rule "alert_#{row.rowNumber}"
when
#{eventType}(#{rule})
then
alertDecision.setDoAlert(Boolean.TRUE);
end
end template
But the problem with this template is that it fixes the number of conditions and actions (1 in this case). According to my use case, I might have different number of conditions and actions in different rules. Is it possible to create a generic template which can create rules, with different number of conditions and different number of actions in each rule?
Drools templates is just a fancy name for a String template mechanism. You can use whatever template framework you want to create your rules.
Some of the frameworks I've used in the past are:
Manual String concatenation using a StringBuilder
StringTemplate
Velocity
Hope it helps,
The other answer suggesting any String template framework is correct; alternatively, if you want a pure Java-based solution, you may want to consider writing your rule dynamically with code using the Executable Model DSL.
You can reference this blog post which has link to references and examples how to use it.
How can we generate a decision report in Drools like the OPA Decision Report.
I've tried to check the drools websites and all. But I couldn't find any concrete information regarding this topic.
You'll have to enable all your rules to report that they are fired.
You can do this by adding (e.g.) the output of a log file entry to the rules' right hand side (or even a simple println to some text file).
A more generic way can be achieved by adding an event listener. A "rule fired" event can then access the rule to retrieve a metadata item and write an entry to a log, or file, or store it in a list or whatever. Obviously this is cleaner and safer (you'll detect a missing metadata entry) and more flexible.
My white paper on rules design patterns describes a technique where you write rule to keep track of individual conditions being met by some fact, and at the end of rules firing or not, you can assess what isn't fulfilled. It requires more work than the "all-or-nothing" rule, but it isn't prohibitive (I think).
I am trying to come up with a mechanism in ODM to enable or disable a rule based on some input parameters like sales-zone, type of product and 6 or 7 other parameters. I don't want to put all these 7 parameters into the condition within the rule since that would reduce the reusability of the rules.
Are there any features available in ODM that can be used for this? Are there any techniques widely used in the BRMS community for such problems?
You can probably make use of rule selection using IRL at rule task level. Write a function which will determine whether the rule is effective or not for this input param. We are using this strategy. See the below screenshot.
I hope this may help you out. Happy Rule Development. :)
You could extend the extension meta data model and add a property that can be set on the rule to indicate the sales zone associated with the rule. Then on the rule task on the rule flow, use a dynamic select to include or exclude rules that have the property set.
However be aware that with lots of rules, dynamic selects can cause performance issues potentially.
I have a scenario wherein I need to add rules to a rule engine dynamically.
What if I add same rule twice/multiple times?
I am not able to get exact behavior of Drools by doing POC(I am a newbie to Drools).
Also, if a rule once inserted remain in knowledgeBase until I explicitly remove it?
You cannot add the save rule twice (which is sufficient to rule out "multiple times"). If it is the "same", it simply replaces the previous "same" rule. If only the titles differ, then (it isn't the same rule and) you have two rules with the same LHS and the same RHS. This may, or may not, produces the same reaction a second time: this depends on what the RHS does or does not.
You can and should clarify these things by reading the documentation and/or experimenting with a simple setup.
Today I've been presented with a fun challenge and I want your input on how you would deal with this situation.
So the problem is the following (I've converted it to demo data as the real problem wouldn't make much sense without knowing the company dictionary by heart).
We have a decision table that has a minimum of 16 conditions. Because it is an impossible feat to manage all of them (2^16 possibilities) we've decided to only list the exceptions. Like this:
As an example I've only added 10 conditions but in reality there are (for now) 16. The basic idea is that we have one baseline (the default) which is valid for everyone and all the exceptions to this default.
Example:
You have a foreigner who is also a pirate.
If you go through all the exceptions one by one, and condition by condition you remove the exceptions that have at least one condition that fails. In the end you'll end up with the following two exceptions that are valid for our case. The match is on the IsPirate and the IsForeigner condition. But as you can see there are 2 results here, well 3 actually if you count the default.
Our solution
Now what we came up with on how to solve this is that in the GUI where you are adding these exceptions, there should run an algorithm which checks for such cases and force you to define the exception more specifically. This is only still a theory and hasn't been tested out but we think it could work this way.
My Question
I'm looking for alternative solutions that make the rules manageable and prevent the problem I've shown in the example.
Your problem seem to be resolution of conflicting rules. When multiple rules match your input, (your foreigner and pirate) and they end up recommending different things (your cangetjob and cangetevicted), you need a strategy for resolution of this conflict.
What you mentioned is one way of resolution -- which is to remove the conflict in the first place. However, this may not always be possible, and not always desirable because when a user adds a new rule that conflicts with a set of old rules (which he/she did not write), the user may not know how to revise it to remove the conflict.
Another possible resolution method is prioritization. Mark a priority on each rule (based on things like the user's own authority etc.), sort the matching rules according to priority, and apply in ascending sequence of priority. This usually works and is much simpler to manage (e.g. everybody knows that the top boss's rules are final!)
Prioritization may also be used to mark a certain rule as "global override". In your example, you may want to make "IsPirate" as an override rule -- which means that it overrides settings for normal people. In other words, once you're a pirate, you're treated differently. This make it very easy to design a system in which you have a bunch of normal business rules governing 90% of the cases, then a set of "exceptions" that are treated differently, automatically overriding certain things. In this case, you should also consider making "?" available in the output columns as well.
One other possible resolution method is to include attributes in each of your conditions. For example, certain conditions must have no "zeros" in order to pass (? doesn't matter). Some conditions must have at least one "one" in order to pass. In other words, mark each condition as either "AND", "OR", or "XOR". Some popular file-system security uses this model. For example, CanGetJob may be AND (you want to be stringent on rights-to-work). CanBeEvicted may be OR -- you may want to evict even a foreigner if he is also a pirate.
An enhancement on the AND/OR method is to provide a threshold that the total result must exceed before passing that condition. For example, putting CanGetJob at a threshold of 2 then it must get at least two 1's in order to return 1. This is sometimes useful on conditions that are not clearly black-and-white.
You can mix resolution methods: e.g. first prioritize, then use AND/OR to resolve rules with similar priorities.
The possibilities are limitless and really depends on what your actual needs are.
To me this problem reminds business rules engine where there is no known algorithm to define outputs from inputs (e.g. using boolean logic) but the user (typically some sort of administrator) has to define all or some the logic itself.
This might sound a bit of an overkill but OTOH this provides virtually limit-less extension capabilities: you don't have to code any new business logic, just define a new rule set.
As I understand your problem, you are looking for a nice way to visualise the editing for these rules. But this all depends on your programming language and the tool you select for this. Java, for example, has JBoss Drools. Quoting their page:
Drools Guvnor provides a (logically
centralized) repository to store you
business knowledge, and a web-based
environment that allows business users
to view and (within certain
constraints) possibly update the
business logic directly.
You could possibly use this generic tool or write your own.
Everything depends on what your actual rules will look like. Rules like 'IF has an even number of these properties THEN' would be painful to represent in this format, whereas rules like 'IF pirate and not geek THEN' are easy.
You can 'avoid the ambiguity' by stating that you'll always be taking the first actual match, in other words your rules have a priority. You'd then want to flag rules which have no effect because they are 'shadowed' by rules higher up. They're not hard to find, so it's something your program should do.
Your interface could also indicate groups of rules where rules within the group can be in any order without changing the outcomes. This will add clarity to what the rules are really saying.
If some of your outputs are relatively independent of the others, you will also get a more compact and much clearer table by allowing question marks in the output. In that design the scan for first matching rule is done once for each output. Consider for example if 'HasChildren' is the only factor relevant to 'Can Be Evicted'. With question marks in the outputs (= no effect) you could be halving the number of exception rules.
My background for this is circuit logic design, not business logic. What you're designing is similar to, but not the same as, a PLA. As long as your actual rules are close to sum of products then it can work well. If your rules aren't, for example the 'even number of these properties' rule, then the grid like presentation will break down in a combinatorial explosion of cases. Your best hope if your rules are arbitrary is to get a clearer more compact presentation with either equations or with diagrams like a circuit diagram. To be avoided, if you can.
If you are looking for a Decision Engine with a GUI, than you can try this one: http://gandalf.nebo15.com/
We just released it, it's open source and production ready.
You probably need some kind of inference engine. Think about doing it in prolog.