Asynchronous linking in a service oriented architecture stuff happens
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Asynchronous Linking in a Service—Oriented Architecture (“Stuff Happens”). Sanjay Vivek, Kenneth K. Tso, Mark K. Thompson, David C. De Roure Department of Electronics and Computer Science, University of Southampton UK. Position.

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Asynchronous Linking in a Service—Oriented Architecture (“Stuff Happens”)

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Asynchronous linking in a service oriented architecture stuff happens

Asynchronous Linking in a Service—Oriented Architecture(“Stuff Happens”)

Sanjay Vivek, Kenneth K. Tso, Mark K. Thompson, David C. De Roure

Department of Electronics and Computer Science, University of Southampton UK


Position

Position

  • Service—Oriented Architectures (SOA) decouple components in space

  • Message—Oriented Middlewares (MOM) decouple components in time

  • This double decoupling is useful…


Motivation

Motivation

  • Threefold motivation for asynchronicity

    • The ad hoc world where you walk into the room and stuff happens

    • The poor-performing-proxy world where the time-boundedness of link processing intrudes

    • The live-action, live-media worlds where the comms model is notification-based


Position1

Position

  • Service—Oriented Architectures (SOA) decouple components in space

  • Message—Oriented Middlewares (MOM) decouple components in time

  • This double decoupling is useful for:

    - mobile; lightweight; pervasive OHSes

    - existing systems where synchronicity hurts

    - linking from streamed media


Overview

Overview

  • Service–Oriented Architectures

  • Asynchronous Interaction

  • Example with MQe™ and Auld Linky

  • Thoughts


Service oriented architectures

Service—Oriented Architectures

  • SOA enable service components residing on a network to be published, discovered, and invoked by each other

  • Enables seamless interop between distributed components

  • Typically 3 components:

    • Service Provider

    • Service Broker

    • Service Requester

  • With 3 functions:

    • Find

    • Bind

    • Interact


Web services example stack

Web Services Example Stack

  • Define interface to service components (e.g. Link service interface)

  • Publish service description in repository

  • Interact with other services to form complex applications

Workflow (WSFL)

Discovery (UDDI)

Description (WSDL)

Packaging (SOAP,XML)

Transport (HTTP, Jabber)

Network (TCP/IP)


Asynchronous interaction

Asynchronous Interaction

  • Transaction-based fire-and-forget messaging

  • Queues of messages (function calls) directed towards services

  • Example: IBM’s MQSeries Everyplace (MQe)

    • Assured once-only delivery

    • Messages queued and routed toward end-points

    • Contextual triggers for additional functionality

    • Lightweight in speed and size


Example using mqe and auld linky

N

Auld Linky

linkbases

Example using MQe™ and Auld Linky

before

HTTP

DLS

HTTP

HTTP


Example using mqe and auld linky1

Example using MQe™ and Auld Linky

  • Ported Auld Linky’s HTTP interface for Linkbase query/update to a Web Service

  • Wrapped service with an MQe Custom Queue

  • HTTP Proxy-based DLS interacted with Linky using HTTP; now issues SOAP calls which are transported through MQe queues


Example using mqe and auld linky2

N

Auld Linky’

queues

queues

linkbases

Example using MQe™ and Auld Linky

after

HTTP

DLS’

SOAP

HTTP

MQe QM

MQe QM

SOAP/MQe

SOAP/HTTP


Issues with the dls mqe linky example

Issues with the DLS-MQe-Linky Example

  • Latency and QoP control

    • Additional overhead in the path from query source to query target

    • Application context can determine prioritisation of link resolution events

  • Modality of link resolution has shifted

    • Non-availability of clients results in requests/responses being “buffered”, but for how long?

  • Concurrency; Resilience; Query-routing…


Thoughts

Thoughts

  • Is such decoupling good for the soul?

    • Asynchronicity; Dislocation

  • Different Link service interaction

    • Notifications and the “Null Query”

  • Other OHS layers and functions, beyond Links

    • Linking is fun, but executable structures (with continuations) could be more-so(!)


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