decision tables as a programming tool
DESCRIPTION
Decision tables compared with “conventional” programming languages. - How decision tables can be used but as a practical and efficient programming tool, not just as visual representations of complex logical processing - Shortcut compact coding techniques - Comparisons for simple truth and complex logic codingTRANSCRIPT
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Howard Rogers Director Technical Support
Decision Tables as a
Programming tool
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Agenda
• A brief history
• Decision table structures
• Rule formats
• Rule redundancy, reduction and optimisation
• Relevance testing
• Some practical examples
• Current examples of use
• Future developments
• Questions and Answers
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Speaker
• Statistics & Operation Research
• UK National Health Service
• 35 years IT
• Decision table based languages and compilers
• Query & reporting tools
• Generic file & database access
• Brief interlude with RTPI
• Technical support
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History • NASA
• Morgan Crucible – LITA – List &Tabulate
• TABN for ICL 1900 series mainframes
• (DE)TAB-360 for IBM System/360
• UNITAB for UNIVAC
• HTAB for Honeywell
• TAB-11 for RSTS/E on PDP-11
• FTL6/DTPL for ICT 1900 series
• RPL-11 for RT-11, RSTS/E, RSX-11 on PDP-11
• RPL-3 for IBM System/3
• Filetab-D for x86 and PDP-11, OpenVMS VAX
• FPL - IBM PCs and compatibles.
• RPL, Rapid-Expert and expertGenius extended syntax for Microsoft
Windows, Unix, Linux and OpenVMS,VAX, Alpha & Itanium
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History
• Excel – query tables
• COPE – Translate DTs to COBOL
• LogicGEM – Translate to BASIC,C, C++, FORTRAN, Pascal etc etc
• CCIDE – Pre-processor for BASIC, JAVA, CC, C++, BASH, QB, VB,
and EX(euphoria)
• Silk (Simple In-line Logic Kompiler) converting decision tables to
Cobol code and vice versa.
• PASPREP – Pascal preprocessor
• Many many others
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Decision table structure
• Conditions
• Actions
• Condition rules
• Action rules
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Single Condition Decision Table
Condition Stubs Rules
Action Stubs Actions
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Quantity > 100 Y N
Apply 20% Discount X -
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Decision Tables
Horizontal vs Vertical Condition Stubs Action Stubs
Rules Actions
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Quantity > 100 Apply 20% Discount
Y N
X -
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Multiple Single Decision Table
Condition Stubs Rules
Action Stubs Actions
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Quantity > 100 Y Y N N
Cash payment Y N Y N
Apply 20% Discount X - - -
Apply 10% Discount - X - -
Apply 5% Discount - - X -
No discount - - - -
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Multiple Condition DTs
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• Complete True/False Y N require
2^Conditions rules
• 3 Conditions – 8 rules
• 4 Conditions – 16 rules
• etc
• Use of “-” to reduce completeness
• Practical limit 32
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Five Conditions – One rule
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Initially no discount
Quantity > 100 Y -
Cash payment Y -
Credit_check Y -
Product type is laptop Y -
Employee N -
Apply 5% Discount X -
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Multiple Section Decision Table
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Quantity > 100 Y Y N N
Cash payment Y N Y N
Apply 20% Discount X - - -
Apply 10% Discount - X - -
Apply 5% Discount - - X -
No discount - - - -
Discount_amount < $1 Y -
No discount X -
Discount amount > $1000 Y -
Set discount $1000 X -
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Simplifying Decision Tables 1
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1 2 3 4 5 6 7 8
Credit limit exceeded
Y Y Y Y N N N N
Cash payment Y Y N N Y Y N N
Special clearance Y N Y N Y N Y N
Accept order X X X - X X X X
Reject Order - - - X - - - -
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Simplifying Decision Tables 2
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1&2 3 4 5 6 7 8
Credit limit exceeded
Y Y Y N N N N
Cash payment Y N N Y Y N N
Special clearance - Y N Y N Y N
Accept order X X - X X X X
Reject Order - - X - - - -
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Simplifying Decision Tables 3
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1&2 3 4 5&6 7&8
Credit limit exceeded
Y Y Y N N
Cash payment Y N N Y N
Special clearance - Y N - -
Accept order X X - X X
Reject Order - - X - -
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Simplifying Decision Tables 4
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1&2 3 4 567&8
Credit limit exceeded
Y Y Y N
Cash payment Y N N -
Special clearance - Y N -
Accept order X X - X
Reject Order - - X -
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Simplifying Decision Tables 5
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4 123567&8
Credit limit exceeded
Y ELSE
Cash payment N -
Special clearance N -
Accept order - X
Reject Order X -
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Optimising Decision Tables
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1 2 3 4 5 6 7 8
Credit limit exceeded
Y Y Y Y N N N N
Cash payment Y Y N N Y Y N N
Special clearance Y N Y N Y N Y N
Accept order X - X - X X X X
Reject Order - X - X - - - -
2&4 123567&8
Credit limit exceeded
Y ELSE
Special clearance N -
Accept order - X
Reject Order X -
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ELSE Rule
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4 123567&8
Credit limit exceeded
Y ELSE
Cash payment N -
Special clearance N -
Accept order - X
Reject Order X -
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Simplifying Decision Tables –
Extended entry
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TRANSKEY GT MASTKEY Y - - - ELSE
TRANSKEY EQ MASTKEY - Y Y - -
TRANSKEY LT MASTKEY - - - Y -
TRANSTYPE = “I” - - - Y -
TRANSTYPE = “D” - - Y - -
TRANSTYPE = “A” - Y - - -
CALL PROCESS_MATCH - X - - -
CALL PROCESS_MISS - - X - -
CALL PROCESS_ADD - - - X -
CALL NEXT_TRANS - X X X -
CALL NEXT_MAST X X X - -
REPEAT X X X X -
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Simplifying Decision Tables –
Extended entry
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TRANSKEY ? MASTKEY > = = < ELSE
TRANSTYPE = “?” - A D I -
CALL PROCESS_? - MATCH MISS ADD -
CALL NEXT_TRANS - X X X -
CALL NEXT_MAST X X X - -
REPEAT X X X X -
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Ambiguity or Multi-ruling?
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Set discount
Initialise DISCOUNT_PERC
Cash payment Y - - -
Special offer - Y - -
Good credit history - - Y -
DISCOUNT_PERC + ? 5 10 2 -
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Code generation 1
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|--------------------------------------------------|
|--------------------------------------------------|
|# |STATEMENT 1 2 3 4 5 6 7 8 |
|--------------------------------------------------|
|C1 |Cash payment |y |y |y |y |n |n |n |n |
|C2 |Special offer |y |y |n |n |y |y |n |n |
|C3 |Good credit history |y |n |y |n |y |n |y |n |
|==================================================|
|A1 |Discount initialise | | | | | | | | |
|A2 |Discount + 5 |X |X |X |X | | | | |
|A3 |Discount + 10 |X |X | | |X |X | | |
|A4 |Discount + 2 |X | |X | |X | |X | |
|--------------------------------------------------|
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Generation – Nested If/else 1
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{ if ((Cash payment)) { if ((Special offer)) { if ((Good credit history)) { /* rule 1 */ Discount + 5; Discount + 10; Discount + 2; } else { /* rule 2 */ Discount + 5; Discount + 10; } } else { if ((Good credit history)) { /* rule 3 */ Discount + 5; Discount + 2; } else { /* rule 4 */ Discount + 5; } } } else {
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Generation – Nested If/else 2
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if ((Special offer)) { if ((Good credit history)) { /* rule 5 */ Discount + 10; Discount + 2; } else { /* rule 6 */ Discount + 10; } } else { if ((Good credit history)) { /* rule 7 */ Discount + 2; } else { /* rule 8 */ } } } }
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Generation – Case Switch 1
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{ if ((Cash payment)) { if ((Special offer)) { if ((Good credit history)) { rule_number = 1; } else { rule_number = 2; } } else { if ((Good credit history)) { rule_number = 3; } else { rule_number = 4; } } }
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Generation – Case Switch 2
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else { if ((Special offer)) { if ((Good credit history)) { rule_number = 5; } else { rule_number = 6; } } else { if ((Good credit history)) { rule_number = 7; } else { rule_number = 8; } } }
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Generation – Case Switch 3
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switch (rule_number) { case 1: Discount + 5; Discount + 10 ; Discount + 2; break; case 2: Discount + 5; Discount + 10; break; case 3: Discount + 5; Discount + 2; break; case 4: Discount + 5; break;
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Generation – Case Switch 4
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case 5: Discount + 10; Discount + 2; break; case 6: Discount + 10; break; case 7: Discount + 2; break; case 8: break; }
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Generation – Rule List 1
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{ if ( ((Cash payment)) && ((Special offer)) && ((Good credit history)) ) { Discount + 5; Discount + 10; Discount + 2; } if ( ((Cash payment)) && ((Special offer)) && (!(Good credit history)) ) { Discount + 5; Discount + 10; } if ( ((Cash payment)) && (!(Special offer)) && ((Good credit history)) ) { Discount + 5; Discount + 2; } if ( ((Cash payment)) && (!(Special offer)) && (!(Good credit history)) ) { Discount + 5; }
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Generation – Rule List 2
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if ( (!(Cash payment)) && ((Special offer)) && ((Good credit history)) ) { Discount + 10; Discount + 2; } if ( (!(Cash payment)) && ((Special offer)) && (!(Good credit history)) ) { Discount + 10; } if ( (!(Cash payment)) && (!(Special offer)) && ((Good credit history)) ) { Discount + 2; } if ( (!(Cash payment)) && (!(Special offer)) && (!(Good credit history)) ) { } }
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Generation – Rule Mask
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{Mask = 11111111 {if ( Cash payment) Mask AND 11110000; } {if ( Special Offer) Mask AND 11001100; } {if (Good credit history) Mask AND 10101010; } {if (Mask AND 11110000) Discount + 5 ; } if (Mask AND 11001100) Discount + 10; } if (Mask AND 10101010) Discount + 2; }
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Rule masking
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• Succinct code
• Reduces repetition of condition testing
• Reduced repetition of action code
• Fast execution
• No frequency/cost weighting of rules
needed
• All conditions are evaluated
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Relevance Testing
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AGE > 50 Y - -
CALL ADJUST_COVER Y - -
TRANSKEY LT MASTKEY - Y -
LOOKUP MASTER TRANSKEY - Y -
Some operations require dynamic masking where actions may be performed or I/O occurs
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Relevance Testing
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AGE > 50 Y - -
COVER + 20 R - -
TRANSKEY LT MASTKEY - Y -
DISPLAY “Message” - R -
Dynamic masking again needed when Actions are inserted into condition section of Decision Table using “R”
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Decision table linkage
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CALLs to other DTs or object library routines
CALL Credit_limit_exceeded Y ELSE
CALL Cash_payment N -
CALL Special_clearance N -
CALL ACCEPT_ORDER - X
CALL REJECT_ORDER X -
GOTO link to DT or indirect CALL
CALL Credit_limit_exceeded Y ELSE
CALL Cash_payment N -
CALL Special_clearance N -
GOTO ACCEPT_ORDER - X
CALL_I Variable_name X -
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Requirements of a DT language
• Feature rich language
• Support for multiple data types
• Unmatched data type comparison
• Good string handling/text manipulation
• Access external routines/library functions
• File, database, object and data dictionary
• Callable access from other products
• Source code maintenance, version control
• Compiled and portable execution
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Decision Tables in other products
• Uses GUI in SAP HANA Studio
• SAP Parameter/Database DTs
• Alternate use via Excel spreadsheets
• SMARTS
• OpenRules Engine
• Decision First Modeler
• Drools
• Many more …
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Usage of RPL - expertGenius
• Self compiling
• Cross compiling
• Source of Genius Suite
• Code writing and compiling 4GL and RAD
toolset
• Complete layered application suites
• Reporting – fixed logic
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Genius deployment
• Aerospace factory tracking systems
• Mobile phone billing systems
• Payroll data mining
• HR system ad-hoc querying
• Newspaper distribution system
• Stock control
• Sales order dashboard & EIS
• Web based on-line parts ordering
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CDT Callable Decision Tables
• Simple calculator
• Calculator code
• Tax formula (UK)
• Tax calculator
• Tax code
• CDT Callable access from other
languages and applications
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Future developments
• Extend range of generic database access
• Ports to new architectures
• Macro expansions for FEEL or S-FEEL
• GUI extensions
• CDT Callable access from other
languages and applications
• Cloud based compiler
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Howard Rogers Director Technical Support
Decision Tables as a
Programming tool