1 Evaluation of OCL for Large-Scale Modelling A Different View of the Mondex Smart Card Application Emine G. Aydal, Richard F. Paige, Jim Woodcock University of York

2 AGENDA Motivation Goal Modelling Mondex Modelling issues Validation Test case generation Conclusion Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

3 Alloy (MIT) Event-B (University of Southampton) OCL (University of Bremen) Perfect Developer (Escher Technologies) RAISE (Uni. of UN Macao and TUD) Z (University of York) Based on the monograph that outlined the specifications, refinement and proof details of Mondex in Z (Stepney and Woodcock) Motivation MONDEX : Global e-payment scheme that offers immediate transfer of value without signature or PIN in currencies allowed. First Step in Grand Challenge Program Contribution of this study Model the system from informal requirements by using semi-formal techniques Perform model-based testing on formally-verified versions of Mondex Assess the value added Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation| Conclusion

4 Goal Test cases derived from models before development stage Model-based testing of formally verified s/w Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation| Conclusion

5 Goal Model Mondex by using UML and OCL Diagrams Invariants Pre/post-conditions Validate the model through scenarios Explore the relationship between test case generation and assertion-based scenarios Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

6 Modelling Mondex No.Module Name M1Payment M2Logging M3Recovery M4Currency Management M5Operational Control M6Data Display and Customisation Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

7 Modelling Mondex Modelling Language : UML enriched with OCL expressions Tool : UML Specification Environment (USE) Use case diagrams and use scenarios Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

8 Modelling Mondex 8 Classes 30 Invariants 31 Operations 197 Pre/post-conditions Traceability Matrix Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

9 Modeling issues Constants Derived Parameters May be fixed at a later stage in the development or during application loading Currently no support for constants Example: inv iNoLanguages: self.languages->size() <= cNoLanguages Prefixed with ‘/’ in UML (‘_’ in USE) Supported by OCL Not integrated into the OCL tools Workaround : create invariants ensuring the correct calculation of the derived attributes inv iNoUnusedException : _NumberOfUnusedExceptions = cNoException - exceptionlogs->size() Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

10 Modeling issues Constants Derived Parameters Invariants Pre/post-conditions (assertions) No consistency check Restricting invariants No tool support yet (OCL Compiler v2.0) Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

11 Modeling issues Pre/Post-conditions State Checking Self.OclInState(Unlocked) Self.LockingState = ‘Unlocked’ Messaging: HasSent Operator (‘^’) post ChangePersonalCodePost1: %Personal Code changes successfully or (PersonalCode = and Self^ChangeTheStateToLockedOut and result = false) Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

12 Modeling issues Pre/Post-conditions Frame Variables Set (FVS) Distinct set of variables read/written by each operation Determination of these variables Management of the post values of these variables Assumption : All the variables not included in FVS of an operation stay unchanged after the execution of that operation No tool support Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion

13 Validation of the model Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion Overall Objective: The model behaves as expected when an instance of the model is executed under certain conditions. There is at least one instance of the model that satisfies all the invariants. There is at least one instance of the model that allows each operation to run successfully, i.e. preconditions and postconditions of the operation are satisfied and the instance does not conflict with any of the invariants.

14 Validation of the model Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion Scenario: An instance of the model that serves a purpose, i.e. that satisfies a property. Base object model : An initial, stable instance of the model that satisfies all the invariants. Scenario structure Setting/creation of FVS Access the operation (Precondition check) Modification/Deletion of FVS Exit the operation (Postcondition check)

15 Validation of the model Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion Creation of scenarios that validate operations Execution of scenarios Immediate feedback by the tool Drawback: Finding the set of frame variables and their values in order to satisfy assertions of a certain operation

16 Test Case Generation Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion Assertions ensure the correct functioning of operations. So why not using these critical points in test case generation? Idea: Find scenarios that violates each assertion of each operation.

17 Test Case Generation Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion Existing research: In order to validate a model, generate automatic snapshots of a model by using ASSL (A Snapshot and Sequence Language) in USE [Gogolla,2003] Based on invariant conflict. Each invariant is addressed separately by feeding the system with its reverse.

18 Test Case Generation Motivation | Goal | Modelling Mondex | Modelling Issues | Validation | Test case generation | Conclusion Additional information Scenarios that violate 197 assertions are already created manually. Future work Apply the technique described in [Gogolla,2003] for invariants to assertions. Automate the generation of such scenarios Compare the results of manual and automatic scenario generation Concretise scenarios into test scripts

19 Conclusion Motivation | Goal | Modelling Mondex | Modeling Issues | Validation | Test case generation | Conclusion Modeled a real life application by using OCL. The large number of invariants and assertions provided us ideas in terms of features that needs to be added into OCL tools. The scenarios are a way of validating your model. The fact that scenarios use artifacts of the model supports the validation process. Test case generation and Validation are two processes that may have common grounds.

20 THANK YOU… Motivation | Goal | Modelling Mondex | Modeling Issues | Validation | Test case generation | Conclusion