Modeling and Design of Rule-Based Systems Yonglei Tao.

Modeling and Design of Rule-Based Systems

Yonglei Tao

Key Takeaway Points Business rules are decision-making rules

each consists of conditions and actions to perform when the conditions are met.

A decision table is used to specify business rules check complete, consistent, and non-redundant generate code support test-case generation and test-driven

development enable rules to be updated dynamically

2

Business Rules of an Office Worker

10% Pay Raise

Promotion

Own Office

Stay

Quit

1 2 3 4

Y

x

Y

Y

x

Y-

-

x

N N

N

4 1 1

N

N

-

x

2Rule Count

Decision Table

10% Pay Raise

Promotion Own Office

Stay

Quit

Y

N

Y

Y Stay

N

N

Quit

Decision Tree

3

Decision Table Terminology

10% Pay Raise

Promotion

Own Office

Stay

Quit

1 2 3 4

Y

x

Y

Y

x

Y-

-

x

N N

N

4 1 1

N

N

-

x

2Rule Count

Decision Table

conditionstubs

conditionentry

actionstubs

For checking completeness 4+1+1+2= 23=8

rule number

action entry

indifference or don’t care

4

Limited and Extended Entry

customer

rules covered

request pay

OK order

Rule# 1

>2m

-

3

X

2

<=2m

3

X

reg.

1 2

due payment

X

4

X

new

1

no

5

X

2

no<=2m

new/NR

notnew

Extended entry decision table: non-binary.conditions extend into condition entries.

10% Pay Raise

Promotion

Own Office

Stay

Quit

1 2 3 4

Y

x

Y

Y

x

Y-

-

x

N N

N

4 1 1

N

N

-

x

2Rule Count

Limited entry decision table

5

Systematic Decision Table Construction1. Identify conditions that affect actions2. Identify actions that are affected by conditions3. Draw a table with appropriate rows and

columns4. Enter the conditions and actions into the

condition stubs and action stubs5. Systematically enter the condition values in

the condition entries6. For each condition combination, check the

corresponding action(s). If the actions must be performed in a certain order, use serial numbers to indicate the order

6

Systematic Decision Table Construction

10% Pay Raise

Promotion

Own Office

Stay

Quit

1 2 3 4

Y

x

Y

N

x

NY

Y

Y Y

Y

1 1 1

Y

N

N

1Rule Count

5 6 7 8

N

x

Y

N

x

NY

Y

x

N N

Y

1 1 1

N

N

N

x

1

x x

7

Progressive Decision Table Construction Enter the conditions one at a time and

completes a rule as early as possible

promotedwork

interest

10% raise

ownoffice

stay

quite

Y

N

NNN

YYY

8

Progressive Decision Table Construction1) Draw a table of required rows and columns 2) Enter the actions into the action stubs.

Stay

Quit

Rule Count

Rule #

9

Progressive Decision Table Construction3) Enter one of the conditions into condition stub

and one of the condition value into the condition entry. Save the remaining values.

Promotion

1

Y

Remaining Values

Stay

Quit

Rule Count

Rule #

N

10

Progressive Decision Table Construction4) If the rule can lead to an action then

enter “-” in the remaining conditions check the appropriate action entries begin a new rule: copy all the condition entries of the previous rule

except the last condition enter one of the remaining values of the last condition

Promotion

1

Y

Remaining Values

Stay

Quit

Rule Count

Rule #

N

11

Progressive Decision Table Construction else

enter another condition and one of its values save the remaining values

>=10% Raise Y N

Promotion

1

Y

Remaining Values

Stay

Quit

Rule Count

Rule #

N

12

Progressive Decision Table Construction5) Repeat the above step

promotedwork

interest

10% raise

ownoffice

stay

quite

Y

N

NNN

YYY

>=10% Raise Y N

Promotion

1

Y

Remaining Values

Stay

Quit

Rule Count

Rule #

N

X

--

--

2

Y

N

--

--

X

3

N

Y N

Work Interest Y N

--

X

4

N

Y

N

Own Office Y N

X

5

N

Y

N

N

X

13

Quality Aspect of Decision Table Completeness

are there missing rules? check by the rule count

are there missing conditions or actions? application dependent

Consistency is there more than one rule with the same

condition combination but different actions? does a rule have conflicting actions?

Non-redundancy can/should some rules be eliminated or merged?

14

Rule#

Rule Count

Stay

Quit

10% raise Y

X

promoted Y1

Y

N

X

2N

Y

- - Y

X

3

work interest

N

Y

N

X

Y

4

- - -own office

4 2 14 1 2 1 1

N

Y

N

X

N

5

N

N

Y

X

-

6

N

N

N

X

Y

7

N

N

N

X

N

8

Are there redundancies in the decision table?What problems can be caused by redundancy?Is there a systematic way to detect and remove redundancies?

Decision Table Redundancy

15

Decision Table Redundancy Problems

can cause inconsistency if one place is modified and the other is not, or

modified differently the code is more tedious

and more difficult to understand and maintain

Benefits to removal shorter and more

efficient code code is easier to

comprehend will not cause

redundancy related inconsistency

Removing decision table redundancies is called “decision table consolidation.”

16

Decision Table Consolidation

Rule#

Rule Count

Stay

Quit

10% raise Y

X

promoted Y1

Y

N

X

2N

Y

- - Y

X

3

work interest

N

Y

N

X

Y

4

- - -own office

4 2 14 1 2 1 1

N

Y

N

X

N

5

N

N

Y

X

-

6

N

N

N

X

Y

7

N

N

N

X

N

8

rule 4: !promoted & 10% raise & !work interest & own office ==> stay

rule 7: !promoted & !10% raise & !work interest & own office ==> stay

17


rules 4+7: (!promoted & !work interest & own office) ==> stay

Rule#

Rule Count

Stay

Quit

10% raise Y

X

promoted Y

1

Y

N

X

2

N

Y

- - Y

X

3

work interest

N

Y

N

X

Y

4

- - -own office

4 2 14 1 2 1 1

N

Y

N

X

N

5

N

N

Y

X

-

6

N

N

N

X

Y

7

N

N

N

X

N

8 Rule#

Rule Count

Stay

Quit

10% raise Y

X

promoted Y

1

Y

N

X

2

N

Y

- - Y

X

3

work interest

N

--

N

X

Y

4

- - -own office

4 2 24 1 2 1

N

Y

N

X

N

5

N

N

Y

X

-

6

N

N

N

X

N

8

Rule 7 deleted.Rule 4 changed.

18


Rule#

Rule Count

Stay

Quit

10% raise Y

X

promoted Y

1

Y

N

X

2

N

Y

- - Y

X

3

work interest

N

--

N

X

Y

4

- - -own office

4 2 24 1 2 1

N

Y

N

X

N

5

N

N

Y

X

-

6

N

N

N

X

N

8

Rules 5 and 8 differ on only one condition. So they can be merged.

Rule#

Rule Count

Stay

Quit

10% raise Y

X

promoted Y

1

Y

N

X

2

N

Y

- - Y

X

3

work interest

N

--

N

X

Y

4

- - -own office

4 2 24 2 2

N

--

N

X

N

5

N

N

Y

X

-

6

Rule 8 deleted and rule 5 changed.

19

Consolidation Algorithm

2 or more unmarked rules differ on only 1

condition?

1 of the rules has “-” for that condition?

delete the otherrules

Halt

Do therules include all

cases for thatcondition?

replace the rules with 1 that has “-” for that condition

Y

YY

N

N

N

mark the rules as visited

20

Consolidation Algorithm Decision Table

>2 or more unmarked rules differ on 1 condition?

1 of the rules has “-” for condition?

the rules include all cases for condition?

Rule Count

delete the other rules

replace rules with one with “-” for condition

go to this decision table

halt

Rule # 1 2 3 4

Y YY

Y

Y

N

N

N

N --

-- --

X

X

X

X X

X

2 1 1 4

21

Code Generation from Decision Table First, arrange the rows and columns so that the

condition rows have increasing frequencies of alternating condition values

Draw a tree to highlight the alternating columns

>1 rule differ on 1 condition?



Rule Count

delete the other rulesreplace rules with one with “-” for conditiongo to this decision table

halt

Rule # 1 2 34

Y YY

Y

Y

N

N

N

N--

----

X

X

X

X X

X

2 1 14

22

Code Generation>1 rule differ on 1 condition?



Rule Count

delete the other rulesreplace rules with one with “-” for conditiongo to this decision table

halt

Rule # 1 2 34

Y YY

Y

Y

N

N

N

N--

----

X

X

X

X X

X

2 1 14

while (true) doif (not >1 rule differ on 1 condition) then breakelse if (1 of the rules has “--” for the condition) then delete the other rules else if (the rules include all cases) then replace rules with one with “--” for that condition

end23

Test Case Generation Decision tables are commonly used to

generate test cases for cause-effect testing Each rule is a test case

identify the component under test initialize the input with appropriate condition

values check the output of the actions

Support unit testing and system testing

24

Decision Tree

>1 rule differ on 1 condition?

Y

N Halt


Y

N


Y replace rules with one with “-” for condition;go to this table

delete the other rulesgo to this table

N go to this table

Decision tree is another method to specify process logic.

25

Class Exercise Using the consolidation algorithm decision

table, consolidate the following decision table.

More than $1M business/yr?

Good payment history?

With us more than 10 years?

Priority treatment

Normal treatment

1 2 3 4

Y

x

Y

N

x

NY

Y

Y Y

Y

1 1 1

Y

N

N

1Rule Count

5 6 7 8

N

x

Y

N

x

NY

Y

x

N N

Y

1 1 1

N

N

N

x

1

x

x

26

Competition of Telephone Companies In the 1990s, U.S. telephone companies (AT&T,

MCI, GTE) competed for customers intensively They offered discount plans to attract customers Each new plan required modification of conditional

statements of the computer program It required a lot of time to change, compile, test

and debug the computer program One company adopted a technology that gave it a

competitive advantage The technology is an application of the

interpreter pattern

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Modeling and Design of Rule-Based Systems Yonglei Tao.

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