1. OHS2002, UMD 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

2. OHS2002, UMD Position n Service—Oriented Architectures (SOA) decouple components in space n Message—Oriented Middlewares (MOM) decouple components in time n This double decoupling is useful…

3. OHS2002, UMD Motivation n Threefold motivation for asynchronicity u The ad hoc world where you walk into the room and stuff happens u The poor-performing-proxy world where the time- boundedness of link processing intrudes u The live-action, live-media worlds where the comms model is notification-based

4. OHS2002, UMD Position n Service—Oriented Architectures (SOA) decouple components in space n Message—Oriented Middlewares (MOM) decouple components in time n This double decoupling is useful for: - mobile; lightweight; pervasive OHSes - existing systems where synchronicity hurts - linking from streamed media

5. OHS2002, UMD Overview n Service–Oriented Architectures n Asynchronous Interaction n Example with MQe™ and Auld Linky n Thoughts

6. OHS2002, UMD Service—Oriented Architectures SOA enable service components residing on a network to be published, discovered, and invoked by each other n Enables seamless interop between distributed components n Typically 3 components: u Service Provider u Service Broker u Service Requester n With 3 functions: u Find u Bind u Interact

7. OHS2002, UMD Web Services Example Stack n Define interface to service components (e.g. Link service interface) n Publish service description in repository n Interact with other services to form complex applications Network (TCP/IP) Transport (HTTP, Jabber) Packaging (SOAP,XML) Description (WSDL) Discovery (UDDI) Workflow (WSFL)

8. OHS2002, UMD Asynchronous Interaction n Transaction-based fire-and-forget messaging n Queues of messages (function calls) directed towards services n Example: IBM’s MQSeries Everyplace (MQe) u Assured once-only delivery u Messages queued and routed toward end-points u Contextual triggers for additional functionality u Lightweight in speed and size

9. OHS2002, UMD Example using MQe™ and Auld Linky DLS N Auld Linky linkbases HTTP before

10. OHS2002, UMD Example using MQe™ and Auld Linky n Ported Auld Linky’s HTTP interface for Linkbase query/update to a Web Service n Wrapped service with an MQe Custom Queue n HTTP Proxy-based DLS interacted with Linky using HTTP; now issues SOAP calls which are transported through MQe queues

11. OHS2002, UMD Example using MQe™ and Auld Linky DLS ’ N queues Auld Linky ’ linkbases HTTP SOAP after MQe QM queues MQe QM SOAP/MQe SOAP/HTTP

12. OHS2002, UMD Issues with the DLS-MQe-Linky Example n Latency and QoP control u Additional overhead in the path from query source to query target u Application context can determine prioritisation of link resolution events n Modality of link resolution has shifted u Non-availability of clients results in requests/responses being “buffered”, but for how long? n Concurrency; Resilience; Query-routing…

13. OHS2002, UMD Thoughts n Is such decoupling good for the soul? u Asynchronicity; Dislocation n Different Link service interaction u Notifications and the “Null Query” n Other OHS layers and functions, beyond Links u Linking is fun, but executable structures (with continuations) could be more-so(!)