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.
Related
I have couple of individual rules. Now for example, I have 3 different set of rules to be executed. Based on the input parameters, at any point a set of rules are to be executed. Let's say in the first set/group there are 5 rules, in the second set/group there are 7 rules and in the third set/group there are 5 rules. Now all these sets might have common rule(s) and I want to refer them instead of having the rule written 3 times in each of the set. How can this be achieved in drools? Tomorrow if I have make an update, I should be able to make the change to the rule only once and this change should reflect in all the sets. Kindly advice on this.....
Thanks,
You can use inheritance to reuse rule logic and you can write reusable DSL statements and write your logic in rdslr.
Another good inheritance example with explanations
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.
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.
I would like to design a rules based database engine within Oracle for PeopleSoft Time entry application. How do I do this?
A rules-based system needs several key components:
- A set of rules defined as data
- A set of uniform inputs on which to operate
- A rules executor
- Supervisor hierarchy
Write out a series of use-cases - what might someone be trying to accomplish using the system?
Decide on what things your rules can take as inputs, and what as outputs
Describe the rules from your use-cases as a series of data, and thus determine your rule format. Expand 2 as necessary for this.
Create the basic rule executor, and test that it will take the rule data and process it correctly
Extend the above to deal with multiple rules with different priorities
Learn enough rule engine theory and graph theory to understand common rule-based problems - circularity, conflicting rules etc - and how to use (node) graphs to find cases of them
Write a supervisor hierarchy that is capable of managing the ruleset and taking decisions based on the possible problems above. This part is important, because it is your protection against foolishness on the part of the rule creators causing runtime failure of the entire system.
Profit!
Broadly, rules engines are an exercise in managing complexity. If you don't manage it, you can easily end up with rules that cascade from each other causing circular loops, race-conditions and other issues. It's very easy to construct these accidentally: consider an email program which you have told to move mail from folder A to B if it contains the magic word 'beta', and from B to A if it contains the word 'alpha'. An email with both would be shuttled back and forward until something broke, preventing all other rules from being processed.
I have assumed here that you want to learn about the theory and build the engine yourself. alphazero raises the important suggestion of using an existing rules engine library, which is wise - this is the kind of subject that benefits from academic theory.
I haven't tried this myself, but an obvious approach is to use Java procedures in the Oracle database, and use a Java rules engine library in that code.
Try:
http://www.oracle.com/technology/tech/java/jsp/index.html
http://www.oracle.com/technology/tech/java/java_db/pdf/TWP_AppDev_Java_DB_Reduce_your_Costs_and%20_Extend_your_Database_10gR1_1113.PDF
and
http://www.jboss.org/drools/
or
http://www.jessrules.com/
--
Basically you'll need to capture data events (inserts, updates, deletes), map to them to your rulespace's events, and apply rules.