Decision Tables
Michael Anstis
Core Developer, Red Hat
8th March 2012

Agenda
What are they?
A little theory
Guvnor
Demo
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What are they?
http://images.wellcome.ac.uk/indexplus/image/V0041734.html
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What are they?
Simply a table
"Decision tables are a precise yet compact way to
model complicated logic." wikipedia
Easily understood by humans
Enable quick and easy analysis
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What are they?
http://commons.wikimedia.org/wiki/File:Formal_Place_Setting_12_Course_Dinner.jpg
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What are they?
Sections
Conditions
Condition states
stub
Actions
Action states
stub
Rule identifiers
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What are they?
Layouts - horizontal
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What are they?
Layouts - vertical
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A little theory
Extended Entry
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A little theory
Limited Entry
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A little theory
http://www.flickr.com/photos/ctbto/4926598654/in/photostream/
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A little theory
Expanded form
Guarantee of completeness
Rule for every combination of conditions
The number of columns should equal the product of the
number of states for every condition.
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A little theory
http://www.flickr.com/photos/marcovdz/4520986339/in/photostream/
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A little theory
Contracted form
Contraction is the first optimization
Stage 1 – impossible matches
Stage 2 – merge condition states
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A little theory
Contraction – impossible conditions
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A little theory
Contraction – merge condition states
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A little theory
http://www.flickr.com/photos/worldseriesboxing/6334574625/sizes/z/in/photostream/
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A little theory
Multiple, all hits
Given a 35 year old with 15 years service
1. Rule 1 matches, giving 22 days
2. Rule 5 matches, giving an additional 3 days
3. A total of 25 days is assigned
Supported by default in Drools
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A little theory
Multiple, first hit
Given a 35 year old with 15 years service
1. Rule 4 matches, giving 25 days
2. Rule 6 would match but Rule 4 was the first hit
Can be emulated with Drools using Control Facts
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A little theory
Single hit
Given a 35 year old with 15 years service
1. Rule 3 matches, giving 25 days
2. No other rules match
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A little theory
http://www.flickr.com/photos/kmakice/4713798045/sizes/m/in/photostream/
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A little theory
Validation and verification
Completeness
Redundancy
Conflict
Deficiency
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Guvnor
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Guvnor
Flexible authoring environment
Extend or Limited Entry
Automatic expansion
V&V
Import from Excel
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And now for something completely different...
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