visibility as central abstraction in event based systems
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Visibility as Central Abstraction in Event-based Systems. Event-based Systems. Pub/Sub System. Benefits. We appreciate the loose coupling Indirect addressing, space decoupling Additional degrees of freedom Basic CS solution… Event-based: Components control their own state, solely

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event based systems
Event-based Systems

Pub/Sub System

Ludger Fiege, [email protected] Darmstadt, Germany

benefits
Benefits
  • We appreciate the loose coupling
    • Indirect addressing, space decoupling
    • Additional degrees of freedom
      • Basic CS solution…
  • Event-based:
    • Components control their own state, solely
      • Independence
      • Reusability

Ludger Fiege, [email protected] Darmstadt, Germany

event based systems1
Event-based Systems

Pub/Sub System

Ludger Fiege, [email protected] Darmstadt, Germany

drawbacks
Drawbacks
  • Composed functionality is
    • Direct and implicit result of composition
    • No explicit control of coordination
  • 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?

Ludger Fiege, [email protected] Darmstadt, Germany

event based systems regaining control
Event-based SystemsRegaining Control

Pub/Sub System

Ludger Fiege, [email protected] Darmstadt, Germany

scopes

Family 2

advice

advice

Ma

GrandMa

Scopes
  • Scopes constrain the visibility of notifications
    • Visibilityas first-class concept
      • Structure not emulated by namespaces or filters
      • Clients not aware of structure
    • External control of structure: Integration

Family 1

sick

sick

Ma

GrandMa

Ludger Fiege, [email protected] Darmstadt, Germany

fairytale ii a scoped world structuring

Forest

Wolf

Fairytale IIA Scoped World: Structuring

Family 1

Family 2

LRRH

Grand-mother

Mother

Ludger Fiege, [email protected] Darmstadt, Germany

fairytale iii a scoped world information hiding

Forest

Wolf

Fairytale IIIA Scoped World: Information Hiding

advice

Family 1

Family 2

advice

advice

LRRH

Grand-mother

Mother

Ludger Fiege, [email protected] Darmstadt, Germany

fairytale iv heterogeneous world

GermanImmigrants

Pen-

friends

Fairytale IVHeterogeneous World

Forest

Family

Wolf

sick

krank

LRRH

Grand-mother

Mother

Ludger Fiege, [email protected] Darmstadt, Germany

fairytale v lrrh services

Default broadcast semantics not always appropriate

Forest

Family 1

Family 2

Wolf

LRRH

Service

Grand-mother

Dad

Mother

1

2

3

Fairytale VLRRH Services

Default broadcast semantics not always appropriate

Forest

Family 1

Family 2

Wolf

LRRH

Service

Grand-mother

Dad

Mother

1

2

3

Ludger Fiege, [email protected] Darmstadt, Germany

implementation
Implementation
  • Project REBECA:

http://www.gkec.informatik.tu-darmstadt.de/rebeca

  • Prototype of notification infrastructure
    • Scalable content-based filtering
    • Structuring with Scopes
  • Example Applications
    • Stock trading platform
    • Self-actualizing web pages

Ludger Fiege, [email protected] Darmstadt, Germany

slide13

2

Component

Interface

Component

*

DeliveryPolicy

*

SimpleComponent

Scope

SecurityPolicy

SessionScope

EventMappings

UML

Ludger Fiege, [email protected] Darmstadt, Germany

using scopes
Using Scopes
  • Different Implementations of Scopes
    • Not always all configuration options available
    • Adapt/tailored to deployment scenario
  • Up to now: Specification
    • XML description of interfaces
    • Java objects implementing policies
  • Future:
    • Composition languages
    • Functional PL

Ludger Fiege, [email protected] Darmstadt, Germany

contributions
Contributions
  • We started by implementing an event-based middleware
  • Introduce scopes in event-based systems
    • first-class structuring mechanism
    • Obvious benefits
      • Control side effects
    • Address heterogeneity issues
    • Refine event service semantics

Ludger Fiege, [email protected] Darmstadt, Germany

and then
…and then
  • Event-based components
    • Information hiding
    • Composing new components
  • Implemented framework:
    • allows to investigate scopes as new abstraction in event-based systems
    • Software engineering
      • Component languages, Meta Object Protocols
    • Data management
      • Sessions, transactions, notification lifetime
    • Distributed systems
      • Multicast, ordering, group communication

Ludger Fiege, [email protected] Darmstadt, Germany

questions
Questions?

Thank you for listening!

Ludger Fiege

Dep. of Computer Science

TU Darmstadt, Germany

[email protected]

Ludger Fiege, [email protected] Darmstadt, Germany

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