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, fiege@acm.orgTU 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, fiege@acm.orgTU Darmstadt, Germany


Event based systems1
Event-based Systems

Pub/Sub System

Ludger Fiege, fiege@acm.orgTU 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, fiege@acm.orgTU Darmstadt, Germany


Event based systems regaining control
Event-based SystemsRegaining Control

Pub/Sub System

Ludger Fiege, fiege@acm.orgTU 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, fiege@acm.orgTU 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, fiege@acm.orgTU 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, fiege@acm.orgTU Darmstadt, Germany


Fairytale iv heterogeneous world

GermanImmigrants

Pen-

friends

Fairytale IVHeterogeneous World

Forest

Family

Wolf

sick

krank

LRRH

Grand-mother

Mother

Ludger Fiege, fiege@acm.orgTU 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, fiege@acm.orgTU 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, fiege@acm.orgTU Darmstadt, Germany


Visibility as central abstraction in event based systems

2

Component

Interface

Component

*

DeliveryPolicy

*

SimpleComponent

Scope

SecurityPolicy

SessionScope

EventMappings

UML

Ludger Fiege, fiege@acm.orgTU 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, fiege@acm.orgTU 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, fiege@acm.orgTU 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, fiege@acm.orgTU Darmstadt, Germany


Questions
Questions?

Thank you for listening!

Ludger Fiege

Dep. of Computer Science

TU Darmstadt, Germany

fiege@acm.org

Ludger Fiege, fiege@acm.orgTU Darmstadt, Germany