University of Toronto Department of Computer Science

1. Lifting Transformations to Product Lines Rick Salay, Michalis Famelis, Julia Rubin, Alessio Di Sandro, Marsha Chechik University of Toronto Department of Computer Science

2. Product lines • Manage a large number of similar but different artifact variants (products) • Washing Machine Co. +Dry/Delay +Delay +Heat +Dry … Lifting Transformations to Product Lines

3. Feature Model Product line structure Heat • Product line (annotative) represented by • Domain Model – combined parts from all products • Feature Model – shows possible features and restrictions for products • Washing Machine Co. excludes Delay Wash Dry Domain Model +Dry/Delay +Delay +Heat +Dry … Lifting Transformations to Product Lines

4. Feature Model Product line configuration – example 1 Heat • +Heat product • Feature configuration: {Wash, Heat} • Washing Machine Co. excludes Delay Wash Dry +Dry/Delay +Delay +Heat +Heat +Dry … Lifting Transformations to Product Lines

5. Feature Model Product line configuration – example 2 Heat • +Dry/Delay product • Feature configuration: {Wash, Dry, Delay} • Washing Machine Co. excludes Delay Wash Dry +Dry/Delay +Delay +Heat +Dry +Dry/Delay … Lifting Transformations to Product Lines

6. Model product line:washing machine state machine Feature Model Heat Presence Conditions excludes Delay Wash Domain Model Heat Delay [heatEnabled;delayEnabled]/ HeaterOn() Dry Heat Locking Waiting Heat Delay / HeaterOff(); wash.Start(); [not heatEnabled;not delayEnabled]/ wash.Start(); Heat Washing entry/TempCheck() Heat / QuickCool() Unlocking Heat Dry / QuickCool() Dry Dry Dry Drying Lifting Transformations to Product Lines

7. Configuring a model (product) Feature Model Heat excludes Delay Wash Domain Model Heat Delay [heatEnabled;delayEnabled]/ HeaterOn() Dry Heat Locking Waiting Heat Delay / HeaterOff(); wash.Start(); [not heatEnabled;not delayEnabled]/ wash.Start(); Heat Washing entry/TempCheck() Heat / QuickCool() Unlocking Heat Dry / QuickCool() Dry Dry Dry Drying Lifting Transformations to Product Lines

8. +Dry/Delay state machine +Dry/Delay Variant [ delayEnabled] Locking Waiting / wash.Start(); [ not delayEnabled]/ wash.Start(); Washing Unlocking / QuickCool() Drying Lifting Transformations to Product Lines

9. +Dry/Delay state machine +Dry/Delay Variant [delayEnabled] Locking Waiting /wash.Start(); [not delayEnabled]/ wash.Start(); Washing Unlocking / QuickCool() Drying Lifting Transformations to Product Lines

10. Outline • Product lines • Transformations • Why lift transformations to product lines? • Sketch of lifting algorithm • Evaluation • Summary and next steps Lifting Transformations to Product Lines

11. Transformations in Model Driven Engineering (MDE) • Use to convert one artifact into another • For refinement, generating implementations, refactoring, optimization, translation, etc. • Automates mundane tasks and ensures quality • Enables raising level of abstraction in software development WideYellow Lifting Transformations to Product Lines

12. Our goal • Key problem: Transformations written for models cannot be used directly with product lines of models • Ideally we should lift them to product lines - but how? configure configure ? Model Model Product Line Model Model Model Model Lifting Transformations to Product Lines

13. Idea 1 – Avoid lifting transformation Heat • Problems: • Must keep track of transformations to apply • Can’t do analysis of transformation’s effect on product line excludes Delay Wash Dry configure WideYellow +Dry +Dry Lifting Transformations to Product Lines

14. Idea 2: Configure all products and merge Heat Heat • Problems: • Expensive: may be many products! • Merge is non-trivial excludes excludes Delay Delay Wash Wash Dry Dry configure merge WideYellow WideYellow +Dry +Dry WideYellow +Delay +Delay Lifting Transformations to Product Lines

15. Idea 3: Manually lift by re-developing transformation Heat Heat • Problems: • Requires extensive effort • Error-prone excludes excludes Delay Delay Wash Wash Dry Dry Manual Lift WideYellow Lifting Transformations to Product Lines

16. Our contribution: Automate the lift Heat Heat • Benefits • Low cost • Eliminates manual effort • Guarantees correctness excludes excludes Delay Delay Wash Wash Dry Dry Automated Lift WideYellow Lifting Transformations to Product Lines

17. Outline • Product lines • Transformations • Why lift transformations to product lines? • Sketch of lifting algorithm • Evaluation • Summary and next steps Lifting Transformations to Product Lines

18. Example: State machine refactoring transformation Negative Application Condition NAC Applicability Condition: Apply the rule if the LHS matches and no NAC matches Lifting Transformations to Product Lines

19. Applying FoldEntry – example 1 [delayEnabled] NAC Matching Site FoldEntry +Dry/Delay Variant Unlocking Locking Waiting / QuickCool() /wash.Start(); [not delayEnabled] / wash.Start(); Drying Washing No NAC matches – applicability condition passes  Apply rule Lifting Transformations to Product Lines

20. Applying FoldEntry – example 1 +Dry/Delay Variant [delayEnabled] NAC Locking Waiting FoldEntry Washing entry/ wash.Start(); Unlocking / QuickCool() [not delayEnabled] Drying Lifting Transformations to Product Lines

21. Applying FoldEntry – example 2 NAC FoldEntry [heatEnabled]/ HeaterOn() Locking Waiting +Heat Variant Matching Site / HeaterOff(); wash.Start(); NAC Matches – applicability condition fails  Do not apply rule [not heatEnabled] / wash.Start(); Washing entry/TempCheck() / QuickCool() Unlocking Lifting Transformations to Product Lines

22. How to apply FoldEntry to a Product Line? Feature Model Heat excludes Delay Wash Domain Model Heat Delay [heatEnabled;delayEnabled]/ HeaterOn() Dry Heat Locking Waiting Heat Delay / HeaterOff(); wash.Start(); [not heatEnabled;not delayEnabled]/ wash.Start(); Heat Washing entry/TempCheck() Heat / QuickCool() Unlocking Heat Dry / QuickCool() Dry Dry Dry Drying Lifting Transformations to Product Lines

23. Lifting algorithm sketch • Find matching sites in the domain model • Reinterpret rule applicability condition • Rule must be applicable in at least one product • requires SAT check • Reinterpret how to apply the rule • Modify domain model and presence conditions so rule effect only occurs in applicable products Lifting Transformations to Product Lines

24. Feature Model Heat Domain Model excludes [delayEnabled] [heatEnabled;delayEnabled]/ HeaterOn() Delay Wash Locking Waiting Delay Heat / HeaterOff(); wash.Start(); [not heatEnabled;not delayEnabled] /wash.Start(); Dry [heatEnabled]/ HeaterOn() Locking Waiting Washing entry/TempCheck() +Dry/Delay Variant / QuickCool() Heat Delay Unlocking +Heat Variant 1) Matching Site Unlocking / wash.Start(); / HeaterOff(); wash.Start(); 2) Lifted rule applicability condition passes  Apply rule 2) Rule applicable in at least one product? Locking Waiting Heat / QuickCool() Drying / QuickCool() / wash.Start(); /wash.Start(); Washing entry/TempCheck()  +Dry/Delay Variant Drying  +Heat Variant Heat / QuickCool() Unlocking Washing Heat Heat Dry Dry Dry Dry Lifting Transformations to Product Lines

25. Feature Model Heat excludes [delayEnabled] Delay Wash [not heatEnabled;not delayEnabled] /wash.Start(); Dry [heatEnabled]/ HeaterOn() Locking Waiting Domain Model +Dry/Delay Variant +Heat Variant [heatEnabled;delayEnabled]/ HeaterOn() Unlocking / wash.Start(); / HeaterOff(); wash.Start(); Locking Waiting Locking Waiting / QuickCool() / wash.Start(); /wash.Start(); Washing entry/TempCheck()  +Dry/Delay Variant / HeaterOff(); wash.Start(); Drying  +Heat Variant / QuickCool() Unlocking Washing Washing entry/TempCheck(); wash.Start(); / QuickCool() Unlocking 3) Apply rule domain model and update presence conditions Heat / QuickCool() Delay Drying Lifting Transformations to Product Lines

26. Properties of lifting algorithm • Correct • Lifting satisfies the correctness condition • Termination • Lifting preserves rule set termination • Confluence • Lifting preserves rule set confluence • up to product line equivalence Lifting Transformations to Product Lines

27. Outline • Product lines • Transformations • Why lift transformations to product lines? • Sketch of lifting algorithm • Evaluation • Summary and next steps Lifting Transformations to Product Lines

28. Prototype Implementation • Modified the Henshin [Arendt et al.] graph transformation engine to • Use the lifting semantics for rule execution • Use Z3 [Microsoft] for SAT checks via MMTF [U of T] Henshin Graph Transformation Engine (modified) Model Management Tool Framework(MMTF) Eclipse Workbench Z3 SMT Solver Lifting Transformations to Product Lines

29. Application: Car Crash Management Product Line Objective: Illustrate lifting on a more realistic scenario • Benchmark used in modeling studies • 15,360 products (class diagram variants) • 444 elements, 118 presence conditions • Applied to two transformations • (AddGet) Class Diagram to Class Diagram • adds getters to public data members (1 rule) • (C2R) Class Diagram to Relational Database schema • Translates a class diagram to equivalent schema (9 rules) Lifting Transformations to Product Lines

30. Application: Car Crash Management Product Line • Objective: Illustrate lifting on a more realistic scenario • Benchmark used in modeling studies • 15,360 class diagram variants • Applied to two transformations • (C2R) Class Diagram to Relational Database schema • Translates a class diagram to equivalent schema (9 rules) • (AddGet) Class Diagram to Class Diagram • Refactoring that adds getters to public data members (1 rule) Results Some slowdown but much better than applying to all 15,360 products! Lifting Transformations to Product Lines

31. Scalability Study • (RQ) How does lifted rule execution time scale with: • Size of product line (# of features) • Size of transformation rule (# of elements) • Method • Varying product lines: use the S.P.L.O.T. feature model repository • 359 real feature models from 9 to 290 features • Varying rules: use 7 rules of varying sizes from the literature • Problem: domain models/presence conditions hard to find! • Solution: simulate using random rule matching • Tuned various parameters using the Car Crash Product Line example • Details available online Lifting Transformations to Product Lines

32. Results – time vs. features 12 Time seems to increase with rule size and then suddenly drops! 39 13 # of match elements 4 37 20 25 Time increase close to linear with # of features Lifting Transformations to Product Lines

33. Results - # UNSAT vs. features 25 20 37 # of match elements 4 13 39 12 Reason: larger rules have more fast UNSAT results Lifting Transformations to Product Lines

34. Summary • Product lines and transformations help manage software development • But, usingexisting transformations with product lines is a challenge • Possible solutions • Always apply transformation after configuration • extra maintenance, lose analysis capability • Apply transformation to all products and merge • expensive • Manually redevelop transformation for product line • high effort and error prone • Our solution: automated lifting of transformation to product line • lifting reinterprets transformation execution semantics     Lifting Transformations to Product Lines

35. Summary Cont’d • Preliminary evaluation shows a clear benefit • Automation eliminates effort and potential for error • Lifted transformations are slower but orders of magnitude faster than applying to all products • Scales well with increasing feature model size Lifting Transformations to Product Lines

36. Next Steps • More extensive evaluation • Extending the approach • To richer transformation languages • with control flow • pragmatic transformation languages (e.g., ATL) • To richer product line languages • E.g., Common Variability Language Lifting Transformations to Product Lines

37. Thank you Lifting Transformations to Product Lines