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Testing Business Logic begins in Requirements
Paul Vincent
BCS SIGiST – Summer 2015 Conference - Friday 5 June 2015
Some Known Best Practices …
• Agile development(fail early, deliver often)
• Test-driven development(test specification = system specification)
• Model-driven development(formal models are more easily transformed into software)
2. But how can Requirements be Formal?
• Models can be formal
• Example = BPMN process
• Can be validated, simulated,loops detected etc
Decision
Gateway
Task
Ref OMG DMN
3. Decision Models for Requirements
• Decision “models” are not new!
Babylon 1800BC - Mathematical look-up table
5. Decision Models as Requirements
• How can we define a formal model for business logic that Business Analysts can use?
With appropriate notation, methodology and standards?
• Can modelling tools embed appropriate testing to automate tests?
Decision Methodologies
• TDM - The Decision Model (von Halle, Goldberg)• Published, commercially supported, specific notation
• Tooling (BiZZDesign, Sapiens, SAP,…)
• DTM - Decision Table Methodology (Vanthienen)• Published across papers and books, commercially supported
• Tooling (Various) for decision tables
• Decision Management Systems Methodology (Taylor)• Published, commercially supported
• Own tooling (Decision Management Solutions)
Decision Notations
• TDM - The Decision Model (von Halle, Goldberg)• Published, commercially supported, specific notation• Tooling (BiZZDesign, Sapiens, SAP,…)
• OMG DMN - Decision Model and Notation• Published, commercial support starting, specific notation• Tooling (Signavio, DMS, FICO, …)
Case Study: Example using TDM
Determine PolicyRenewal Method
Manual Renewal
Automatic Renewal
Manual or Automatic
Per OMG DMN
•A Decision is the act of applying decision logic to one or more inputs to produce one output
•A Decision Logic is a formal expression that defines the output of a decision with respect to its inputs• A decision logic can be a Computation• Or a Fixed Alternatives Ruleset, represented as a Decision
Table or a Decision Tree• Or it can be an Imported Formulation (e.g. a predictive model
in PMML)
C. Is this complete, no duplications etc?
ALL VALUES TESTED? ALL VALUE COMBINATIONS TESTED? ALL CONCLUSIONS CONSISTENT?
Assumptions for decision modelling for testing1. I know the decision I need to make
(may be re-used across processes)
2. I define a formal / rigorous data model too (name, type, value domain, single/list)• See Data Modelling for Requirements Testing
presentation at some future SIGiST!
For Business Logic requirements…
1. We can model business logic using Decision Models
2. We can verify the completeness + uniqueness of this business logic
For Business Logic requirements…
1. We can model business logic using Decision Models
2. We can verify the completeness + uniqueness of this business logic
3. We can validate the business logic against all possible use cases for each rule family + all links in a decision model of multiple rule families
How useful is this?
• Example 1: a product selection requirement
• Original analysis = 15,000 rows of business logic in Excel
• Decision Modelled = ~220 rows across ~18 decisionsby 6 Business Analysts over 2-3 weeks
How useful is this?
• Example 2: business loan compliance with policy
• Original analysis = spreadsheet of X tabs ofmetrics vs business sector vs threshold levels
• Decision Modelled = Validate-able thresholds vs policies,Side by side comparison of thresholds,
Champion challenger etc
Standards to support this pattern?
• Standardisation effort by OMG DMN• Notation and metamodel
• Can be used with multiple methodologies eg DTM, TDM
• Tooling to support DMN underway
Decision Table Hit PoliciesIndicator Indicator
TermDescription
Single Hit U Unique Only 1 rule matched = DEFAULT POLICY
A Any Many rules can match but matched rules must have same output
P Priority Many rules can match and matched rules can have different outputs; output selected per a prioritised list of possible outputs
F First Many rules can match and matched rules can have different outputs; output selected per ordering of rules
Multi Hit O Output Matched rule outputs are returned in order per a prioritised list of possible outputs
R Rule Matched rule outputs are returned in order per ordering of rules
C Collect No operator Matched rule outputs are returned in arbitrary order
C+ Collect operator(+, <, >, #)
Operator (sum, min, max, count) applied to the outputs and the result returned
C>
C<
C#