1. Ludger Fiege fiege@acm.org joint work with Mira Mezini, Gero Mühl, Alejandro Buchmann Dep. of Computer Science TU Darmstadt, Germany Visibility as Central Abstraction in Event-based Systems

2. Slide 2 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Event-based Systems Pub/Sub System

3. Slide 3 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Benefits n We appreciate the loose coupling –Indirect addressing, space decoupling –Additional degrees of freedom n Basic CS solution… n Event-based: –Components control their own state, solely n Independence n Reusability

4. Slide 4 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Event-based Systems Pub/Sub System

5. Slide 5 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Drawbacks n Composed functionality is –Direct and implicit result of composition –No explicit control of coordination n Control only by adapting components: –Tailor event types/contents –Encode application structure into components  Sacrifice very benefits of event-based style?! Usable as basic programming paradigm?

6. Slide 6 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Event-based Systems Regaining Control Pub/Sub System

7. Slide 7 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Scopes n Scopes constrain the visibility of notifications –Visibility as first-class concept  Structure not emulated by namespaces or filters  Clients not aware of structure –External control of structure: Integration Family 1 Ma GrandMa Family 2 MaGrandMa sick advice

8. Slide 8 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Fairytale II A Scoped World: Structuring Family 1 Forest Wolf Grand- mother Mother LRRH Family 2

9. Slide 9 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Fairytale III A Scoped World: Information Hiding Family 1 Forest Wolf Grand- mother Mother LRRH Family 2 advice

10. Slide 10 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany German Immigrants Pen- friends Fairytale IV Heterogeneous World Family Forest Wolf Grand- mother Mother LRRH krank sick

11. Slide 11 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Fairytale V LRRH Services Family 1 Forest Wolf Grand- mother Mother LRRH Service Dad Family 2 123 Default broadcast semantics not always appropriate Family 1 Forest Wolf Grand- mother Mother LRRH Service Dad Family 2 123 Default broadcast semantics not always appropriate

12. Slide 12 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Implementation n Project R EBECA: http:// www.gkec.informatik.tu-darmstadt.de/rebeca n Prototype of notification infrastructure –Scalable content-based filtering –Structuring with Scopes n Example Applications –Stock trading platform –Self-actualizing web pages

13. Slide 13 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany UML Component SimpleComponent Scope Component Interface * * 2 Session Scope Delivery Policy Security Policy Event Mappings

14. Slide 14 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Using Scopes n Different Implementations of Scopes –Not always all configuration options available –Adapt/tailored to deployment scenario n Up to now: Specification –XML description of interfaces –Java objects implementing policies n Future: –Composition languages –Functional PL

15. Slide 15 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Contributions n We started by implementing an event-based middleware n Introduce scopes in event-based systems –first-class structuring mechanism –Obvious benefits n Control side effects –Address heterogeneity issues –Refine event service semantics

16. Slide 16 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany …and then n Event-based components –Information hiding –Composing new components n Implemented framework: –allows to investigate scopes as new abstraction in event-based systems –Software engineering n Component languages, Meta Object Protocols –Data management n Sessions, transactions, notification lifetime –Distributed systems n Multicast, ordering, group communication –…

17. Slide 17 Ludger Fiege, fiege@acm.org TU Darmstadt, Germany Questions ? Thank you for listening! Ludger Fiege Dep. of Computer Science TU Darmstadt, Germany fiege@acm.org