Disconnected
Introduction u u u XML based Web Services are becoming the norm on the Web Mobile devices using these web service are becoming increasingly popular Mobile Devices use networks that are characterized by frequent disconnections Web Service need to be universally available Need a solution that is transparently deployable and generally applicable
Caches meets the requirements of being transparent deployment and general applicable u Caches are not a new idea, but XML present a new set of challenges, due it vast set of operations and lack of involvement in caching u Solution is not complete !!!! u
System put forward by our friends at Microsoft u u Build the XML cache into a HTTP proxy to improve transparency In disconnected mode, when a request is received return its cached responses. If no response is cached, client timeouts and save the request in write back queue for later replay. Good idea, but has some inherent flaws
Issues in caching XML for Web. Services u u u Caching XML web services does increase the availability of the service However, the availability of the web service is limited due to several issues Providing solutions to these issues will greatly increase the effectiveness and efficiency of the cache and thus the availability of the web service during periods of disconnection
Issues Consistency u Understanding request and response messages u User Experience u
Consistency u u When operating in disconnected mode, strong consistency is not possible But local (weak) consistency is Providing weak consistency involves understanding the interdependencies between operation (difficult!) GOAL: A smart cache manager that can invalidate and/or transform earlier requests
User XP u Ideally, users should have the same experience when disconnected as when they are connected Weak High Compromised Consistency Strong Availability Low User XP uncompromised
User XP: Cache Aware Clients Adding optional attributes to SOAP messages for cache aware clients allowing them to react, notifying users of possible uncertainties… u These attributes can be ignored by cache unaware clients u Thus the systems remains Web. Service independent u
Understanding SOAP Messages u u Despite Std protocols, web service messages deviate considerably in structure Using WSDL correctly formatted responses can be fabricated but not populated with default values Therefore there is a need to extend the WSDL specs to allow the cache/proxy to be aware of the web-service semantics This can be done without effecting current implementations of Web Services
Work Allocation In essence, the core of the project determines to specify extensions to WSDL specifications u Darryl will focus on WSDL extensions which attempt to under the semantics of SOAP messages u Justin will focus on WSDL extensions which determine interdependencies of SOAP messages u
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