2011-03-29 London - Decision tables in depth (Michael Anstis)

drools

Michael Anstis

Decision Tables in depth

Agenda

Overview

Types

Validation & Verification

Transformation

Decision Tables in Guvnor

Roadmap

Summary

Q&A

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A

Overview

Tabular representation of decisions.

Compact way to model large sets of related rules.

The state of a number of conditions determines the execution of a set of actions.

Many variations of the decision table concept exist which look similar at first sight.

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A

Types

Types

Layout Horizontal

Vertical

Limited entry

Extended entry

Categorisation Expanded form, contracted form

Multi-hit, all hits

Multi-hit, first hit

Single hit

Layouts

Horizontal

Layouts

Vertical

Layouts

Limited entry

Layouts

Extended entry

Categorisation

Expanded form

Single column for every condition combination

The number of columns should equal the product of the number of states for every condition.e.g. 3 conditions each with 2 states gives:

2 * 2 * 2 = 8 combinationse.g. 2 conditions each with 3 states and 1 condition with 4 states gives:

3 * 3 * 4 = 36 combinations

Categorisation

Expanded form (continued)

Condition states should be digitised e.g. age: 60 not a free-form integer field

Condition states should be continuouse.g. GOOD: age=18; BAD: age=30

Not essential for expansion but ensures completeness

This guarantee of completeness of condition combinations is one of the main advantages of decision tables.

Categorisation

Expanded form (continued)

Categorisation

Contracted form

Contraction is the first optimisation.

Reduces the number of condition columns.

If the same actions exist for rules covering all condition states for a given condition they can be combined and the condition state becomes irrelevant.

Categorisation

Contracted form stage 1Rules 2 and 3 are impossible conditions

Categorisation

Contracted form stage 2Merge adjacent column groups with identical action parts

Categorisation

Multi-hit, all hits

To get complete result all rules matching need to have their actions executed.

Condition columns are not mutually exclusive

If the Condition columns are not exclusive, some combination of conditions are present in more than one column, which may lead to ambiguity or inconsistency.

Categorisation

Multi-hit, all hits

Given a 35 year old with 15 years service1. Rule 1 matches, giving 22 days2. Rule 5 matches, giving an additional 3 days3. A total of 25 days is assigned

Categorisation


To get complete result the first rule (from left-to-right) matching needs to have its action executed.

Condition columns are not mutually exclusive.

If the Condition columns are not exclusive, some combination of conditions are present in more than one column, which may lead to ambiguity or inconsistency.

Categorisation


Given a 35 year old with 15 years service1. Rule 4 matches, giving 25 days2. Rule 6 would match but Rule 4 was the first hit

Categorisation

Single hit

Each possible combination of conditions matches exactly one, and only one, rule.

Condition columns are mutually exclusive

As the Condition columns are exclusive; combinations of conditions cannot be present in more than one column which eliminates ambiguity and inconsistency.

Classic form if Single-hit is "expanded decision table"; but this can be optimised or contracted.

Categorisation

Single hit

Given a 35 year old with 15 years service1. Rule 3 matches, giving 25 days2. No other rules match

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A


Redundancy

Ambivalence (conflicting)

Deficiency

Mitigation


Redundancy

Duplication

Subsumption

Two rules have the same actions, but one contains additional conditions in which it will succeed. Whenever the more restrictive rule succeeds, the less restrictive rule also succeeds, resulting in redundancy.

Impossible conditionsConditions that do not make sense (e.g. age < 0)


Redundancy - Subsumption


Ambivalence

Contradictory rules

Two (or more) rules have the same conditions but with different actions.

Conflicting rulesAn action for one rule is the opposite of the same action for the other rule.

Ambiguous rulesThe actions are different but not opposite.


Ambivalence

Premium is 500 if applicant age is less than 30

Premium is 300 if Years Without Claim is greater than or equal to 10 years.

Applicant is 29, premium is 500

Applicant has 12 years without claim, premium is 300

Applicant is 29 with 12 years without claim, premium is ?!?


Deficiency

Missing rulesA situation exists in which a particular action is required, but there is no rule that succeeds in that situation and produces the desired conclusion.

Unused input state or domain attribute

Missing knowledgeThe absence of some essential elements from the problem situation.


Mitigation redundancy

Duplication

Cannot occur in the Single-hit decision table, because columns do not overlap.

Subsumption

Cannot occur in the Single-hit decision table, because columns do not overlap.

Impossible conditions

Impossible combinations may still exist.


Mitigation - ambivalence

The single-hit table format avoids such conflicts.

Premium is 500 if applicant age is less than 30

Premium is 300 if Years Without Claim is greater than or equal to 10 years.

Applicant is 29 with 12 years without claim, premium is 300


Mitigation - deficiency

Missing rules

Expanded decision table is exhaustive

All combinations of condition states are included

Unused input state or domain attribute

Expanded decision table is exhaustiveAll combinations of condition states are included

Missing knowledgeValidation of domain model by domain expert

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A

Transformation

Decision Trees

RequirementsDigitised condition states

Each Condition in a column becomes a branch

Multi-hitWalk every path through tree

Single-hitWalk single path through tree

Transformation

Example - Decision Table

Transformation

Example - Decision Tree

Transformation

Paying attention?

Rules 1, 2 and 3, 4 have the same action no matter what the state of Hunger. Therefore they can be contracted...

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A


What do we currently provide?

Vertical layout

Generalised categorisationMulti-hit, all hit; Multi-hit first hit; Single hit

Extended entry

Digitised condition states (enumerated fields)

New decision table editor

Foundation for future work

Condition and rule negation

Cell merging

Cell grouping



Cell merging



Cell grouping



Video demonstration

Demonstration available online at http://vimeo.com/21438537


Generation of DRL

Each row compiles into a separate DRL rule


Generation of DRL

Each row compiles into a separate DRL rule

rule "Row 1 dtable"

dialect "mvel"

when

$person : Person( age < "18" )

then

$person.setHolidayEntitlement( 27 );

end

rule "Row 2 dtable"

dialect "mvel"

when

$person : Person( age >= "18" , age < "45" , lengthOfService < "15" )

then

$person.setHolidayEntitlement( 22 );

end

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A

Roadmap

What does the future hold?

Provision of other layoutsHorizontal

Limited entry

Automated optimisation

Improved support for digitised condition states

Integration of V&V providing visual feedback

Pluggable editors for Model Fact Types

Usability enhancements

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A

Summary

Decision TablesAre an important tool for modelling decisions

Provide a simple, yet powerful, visualisation of decision components

Allow large sets of related rules to be easily worked upon simultaneously

Provide the means to easily validate and verify rules

GuvnorExisting capabilities suitable for most

A solid foundation for the future

A roadmap to become the market leader

Agenda

Overview

Types


Transformation


Roadmap

Summary

Q&A

Useful links

Projecthttp://www.jboss.org/drools

Reference Manualhttp://www.jboss.org/drools/documentation.html

Bloghttp://blog.athico.com/

Mailing Listshttp://www.jboss.org/drools/lists.html

Michael Anstis

Decision Tables in depth

This is the title
Second line of the title

Click to edit the outline text formatSecond Outline LevelThird Outline LevelFourth Outline LevelFifth Outline LevelSixth Outline LevelSeventh Outline LevelEighth Outline LevelNinth Outline Level

This is the chapter title

This is the subtitle

Technology

2011-03-29 London - Decision tables in depth (Michael Anstis)