Weaving Crosscutting Concerns into Live Sequence Charts Using the Play Engine

1. Weaving Crosscutting Concerns into Live Sequence Charts Using the Play Engine Mark Mahoney Tzilla Elrad

2. Scenario Based Behavior • People think in terms of scenarios, not states. • Ivar Jacobson’s recent work on AOSD and use cases lead us to believe that use cases (scenarios) can drive the development of a system with crosscutting concerns. • Live Sequence Charts are used to model scenarios of behavior. • They are inter-object models. • They can be used to synthesize intra-object models.

3. UML Sequence diagrams • Allow weak partial ordering of events. • Very little can be said about what the system actually does: • Which behaviors are mandatory, which behaviors are optional? • How does the system behave when false conditions are encountered? • How does one specify scenarios that must never occur?

4. Live Sequence Charts (LSC) • LSC’s specify ‘liveness’ or things that must occur. • LSC’s have constructs for • Mandatory behavior (hot elements) • Optional behavior (cold elements) • Anti-scenarios (scenarios that should never happen) • Sub-charts • Iteration • Selection

5. Live Sequence Charts (LSC) • LSC’s are ‘played in’ using a look alike GUI front end and a tool called the Play-Engine. • LSC’s are ‘played out’ using the GUI and the Play-Engine. • The Play-Engine monitors system events looking for satisfied pre-charts. • The Play-Engine will identify inconsistencies in system requirements.

6. LSC Example

7. LSC Example

8. LSC’s and Aspect-Orientation • This early work addresses key Aspect-Oriented tenets as they relate to LSC’s: • Pointcut (Pre-chart)- collects the join points where advice should be applied. • Advice (Main Chart)- some action to occur at the join points in a pointcut. • Obliviousness- A single LSC is naturally oblivious to all other LSC’s. • Quantification- Specifying more than one point in a point cut (Pre-chart). There are limitations in the current language.

9. LSC Extensions to Handle Quantification • Proposed Extension to LSC’s • Regular Expressions in the names of objects/classes. • Regular Expressions in the names of methods. • Some similarity between parameterized templates with the exception that LSC’s force action/reaction behavior. Once a join point is encountered the advice must be applied or it is considered a violation of the requirements. • There is not a similar mandatory behavior requirement with templated UML sequence diagrams.

10. Fire Threat Concern (Core Concern)

11. Security Threat Concern (Core Concern)

12. Manager Notification Concern (Crosscutting Concern)

13. Future Work • Things to be worked out: • Before, after, around semantics. • Core LSC’s vs. Aspect LSC’s. • State machine model synthesis with before, after, and around. • Executing environments.

14. References • Damm, W., Harel, D. LSCs: Breathing Life into Message Sequence Charts, Formal Methods in System Design 19:1 (2001), 45-80. • Harel, D., Marelly, R. Specifying and Executing Behavioral Requirements: The Play In/Play-Out Approach Software and System Modeling (SoSyM) 2 (2003), pp. 82-107. • Harel, D. Marelly, R. Come, Let’s Play. Scenario-Based Programming Using LSCs and the Play-Engine. Springer. (2003). • Jacobson, I. Ng, P. Aspect-Oriented Software Development with Use Cases. Addison-Wesley. (2005).