Asynchronous Linking in a Service

1
Asynchronous Linking in a ServiceOriented
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

2
Position

• ServiceOriented Architectures (SOA) decouple
  components in space
• MessageOriented Middlewares (MOM) decouple
  components in time
• This double decoupling is useful

3
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

4
Position

• ServiceOriented Architectures (SOA) decouple
  components in space
• MessageOriented 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

5
Overview

• ServiceOriented Architectures
• Asynchronous Interaction
• Example with MQe and Auld Linky
• Thoughts

6
ServiceOriented 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

7
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)
8
Asynchronous Interaction

• Transaction-based fire-and-forget messaging
• Queues of messages (function calls) directed
  towards services
• Example IBMs MQSeries Everyplace (MQe)
• Assured once-only delivery
• Messages queued and routed toward end-points
• Contextual triggers for additional functionality
• Lightweight in speed and size

9
Example using MQe and Auld Linky
before
HTTP
DLS
HTTP
HTTP
10
Example using MQe and Auld Linky

• Ported Auld Linkys 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

11
Example using MQe and Auld Linky
after
HTTP
DLS
SOAP
HTTP
MQe QM
MQe QM
SOAP/MQe
SOAP/HTTP
12
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

13
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(!)