Decision Tables, Part 2 ~ The Route to Completeness

Ronald G.  Ross
Ronald G. Ross Co-Founder & Principal, Business Rule Solutions, LLC , Executive Editor, Business Rules Journal , and Co-Chair, Building Business Capability (BBC) Read Author Bio       || Read All Articles by Ronald G. Ross

Decision tables are an excellent means to visualize and manage large sets of rules in consolidated fashion.  Scaling up to large rule sets just about demands it.  Even carefully-designed decision tables, however, are prone to anomalies and other problems -- especially if multi-dimensional.  So they must be scrutinized closely, preferably using automated assistance.

Completeness is an example.  Last month's column[1] presented the following rule along with Decision Table C to illustrate multi-dimensional decision tables.


Rule:  The delivery method for an order is to be as in Decision Table C.

Decision Table C 

Decision Criteria

Delivery Method for an Order

Picked Up by Customer

Shipped by Normal Service

Shipped by Premium Service

Rush order

No

Yes

Yes

Order includes fragile item

No

Yes

--

Order includes specialty item

No

No

--

Order includes high-priced item

No

No

--

Order includes item involving hazardous materials

No

Yes

Yes

Category of customer

Silver

Gold

Platinum

Destination of order

--

Local

Remote

How complete is this decision table?  Not very!  Here is a step-by step analysis, preceded by a brief explanation of the table's layout.

Layout.  Decision Table C establishes the basis for determining the delivery method for an order.  Three possible delivery methods (the outcomes) are indicated along the top.  Seven decision criteria appear at left as labels for the rows.  (This table therefore involves seven dimensions.)  Six of these decision criteria are binary (yes, no or local, remote), whereas one, category of customer, involves three possibilities (silver, gold, platinum).  The choice of delivery method for an order depends on what appears in the cells of a column.  A dash ( -- ) in a cell indicates that the associated decision criteria does not matter in determining the outcome; that is, any alternative for that decision criteria will produce the same outcome.

Completeness Analysis.  How complete is Decision Table C?  Here is a step-by-step analysis.

  1. The total number of possible combinations for the instances of the seven decision criteria can be calculated as:  26 x 3 = 192.  This calculation reflects the fact that six of the decision criteria apparently have two alternatives each (yes and no for five of them, and local and remote for the other), whereas the seventh, category of customer, apparently has three (silver, gold, and platinum).

  2. The total number of combinations actually represented in the table can be determined as follows.  Column 2 represents one combination -- each cell has something in it.  Columns 1 and 3 are a bit more complicated because they both have dashes in one or more cells, indicating acceptance of any alternative -- for example, either yes or no.  Column 1 includes one such cell, so that column actually provides the basis for establishing the outcome for two combinations -- one if the cell had had local and one if it had had remote.  Column 3 includes three such cells, so that column actually establishes the basis for 23 or 8 outcomes.  Altogether, the decision table actually establishes the basis for establishing 11 outcomes (2 + 1 + 8 = 11).

  3. Having determined how many combinations the decision table actually addresses (11), we can now determine how many it does not:  192 - 11 = 181.  So some 181 possible combinations have not been addressed at all!  We must therefore conclude this decision table is not very complete.

References

[1]  Ronald G. Ross, "Decision Tables, Part 1 ~ The Route to Consolidated Business Logic," Business Rules Journal, Vol. 6, No. 7 (July 2005), URL:  http://www.BRCommunity.com/a2005/b240.html return to article


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Standard citation for this article:


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Ronald G. Ross , "Decision Tables, Part 2 ~ The Route to Completeness" Business Rules Journal Vol. 6, No. 8, (Aug. 2005)
URL: http://www.brcommunity.com/a2005/b243.html

About our Contributor:


Ronald  G. Ross
Ronald G. Ross Co-Founder & Principal, Business Rule Solutions, LLC , Executive Editor, Business Rules Journal , and Co-Chair, Building Business Capability (BBC)

Ronald G. Ross is Principal and Co-Founder of Business Rule Solutions, LLC, where he actively develops and applies the IPSpeak methodology including RuleSpeak®, DecisionSpeak and TableSpeak.

Ron is recognized internationally as the "father of business rules." He is the author of ten professional books including the groundbreaking first book on business rules The Business Rule Book in 1994. His newest are:


Ron serves as Executive Editor of BRCommunity.com and its flagship publication, Business Rules Journal. He is a sought-after speaker at conferences world-wide. More than 50,000 people have heard him speak; many more have attended his seminars and read his books.

Ron has served as Chair of the annual International Business Rules & Decisions Forum conference since 1997., now part of the Building Business Capability (BBC) conference where he serves as Co-Chair. He was a charter member of the Business Rules Group (BRG) in the 1980s, and an editor of its Business Motivation Model (BMM) standard and the Business Rules Manifesto. He is active in OMG standards development, with core involvement in SBVR.

Ron holds a BA from Rice University and an MS in information science from Illinois Institute of Technology. Find Ron's blog on http://www.brsolutions.com/category/blog/. For more information about Ron visit www.RonRoss.info. Tweets: @Ronald_G_Ross

Read All Articles by Ronald G. Ross

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