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A Modular Approach to Build Structured Event-based Systems

A Modular Approach to Build Structured Event-based Systems. Ludger Fiege Dep. of Computer Science TU Darmstadt, Germany fiege@acm.org. Agenda. Publish/subscribe and Event-based systems Current deficiencies and a solution… Scoping constrains visibility

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A Modular Approach to Build Structured Event-based Systems

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  1. A Modular Approach to Build Structured Event-based Systems Ludger Fiege Dep. of Computer Science TU Darmstadt, Germany fiege@acm.org Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 1

  2. Agenda • Publish/subscribe and Event-based systems • Current deficiencies and a solution… • Scoping constrains visibility • Event mappings cope with heterogeneity • Modular implementation • Conclusion Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 2

  3. n n n Publish/Subscribe Systemsaka Event-based Systems • Set of clients • Communicate with notificatitons • Producers publish notifications • Consumers subscribe to kinds of notifications • Notification service transmits notifications Notification “/Weather/London” Producer 1. P/S Consumer subscribed “/Weather/Berlin” 2. 2. Consumer subscribed to “/Weather/London” “/Weather/*” Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 3

  4. Event-based Systems • Pub/Sub and messaging are implementation techniques • Characteristics of Event-based cooperation: • Initiator of communication: Producer • Addressee: Not specified • No explicit dependencies, loose coupling Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 4

  5. Notification Service Simple Event-based System • Black box specification • Interface description • Interface operations: • Sub(X,F), Unsub(X,F) • Pub(Y,n) • Notify(X,n) Clients X Y F n Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 5

  6. Simple Event-based System Specification • Basedon LTL: • Safety: Notify(X,n)  previously [Pub(Y,n)  Sub(X,F)], n  F • Liveness: Sub(X,F)  eventually (Pub(Y,n)  n  F Notify(X,n)) Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 6

  7. Notification Service Simple Event-based SystemPossible Implementation • Implementation: • Network of brokers • Floodingor content-based filtering, etc. Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 7

  8. Deficiencies of Event-based Systems • Concentration on efficiency, but… • Complexity of large system design and administration disregarded • Flat address space • No information hiding • Lacking module concept Side effects ! Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 8

  9. n n Scopes • Scopes constrain the visibility of notifications • External control of delivery destinations • Visibilityas first-class concept • Structure not only induced by namespaces or filters • Clients are not aware of the scoping structure Scope 1 Scope 2 F F X Y Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 9

  10. n n n n n n Scope Graphs • Clients and scopes are arranged in a DAG • Visibility: v(X,Y)  X=Y  v(Y,X)  X‘ super(X): v(X‘,Y) • v(1,2) v(1,3) v(3,4) • Visibility roots determinerecipients v(X,Y)  Roots(X)  Roots(Y)  {} Vis. roots 2 1 3 4 Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 10

  11. Event System with Scopes • Safety Notify(X,n)  prev. Pub(Y,n)  Sub(X,F) v(X,Y), n  F • Liveness Sub(X,F)  [v(X,Y)  (Pub(Y,n)  n  F  Notify(X,n))] Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 11

  12. Event System with ScopesImplementation • Build on top of a simple system • Client code • Scoped system API • Manages list of vis. roots • Add list of vis. roots to notifications and filters • Simple system API Simple system Scoped system Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 12

  13. Event Mappings • Event mappings • Discard or transform events at scope boundaries • Can be bound to any edge in the scope graph • Scope interfaces • Map notification to  • Constrain Sub() and Pub() of scopes • Heterogeneous environments • Varying event syntax and semantics • Internal vs. external representations Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 13

  14. Scope Interface Example • Assume clients 2,3,4 subscribed to “n” • Visibility is refined: e.g. v(1,4)   n n  n n 4 3 3 n n 1 2 Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 14

  15. Heterogeneity Example n  n´ n  n´ n´ 3 n n 1 2 Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 15

  16. Scoped System with Mappings • Implementation idea: • Graph transformation • Mapping clients n  n´ n  n´ 3 n  n´ n  n´ 3 1 2 1 2 Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 16

  17. Contributions • Scoping in event-based systems • First-class structuring mechanism • Event mappings: Heterogeneity of • Application environment • Event service semantics / implementation • Modular implementation, modularity support • Formal specification of • Simple Publish/subscribe • scoping, mapping extensions Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 17

  18. Questions? Ludger Fiege Dep. of Computer Science TU Darmstadt, Germany fiege@acm.org Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany Slide 18

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