DisconnectedDisconnected

IntroductionIntroduction

XML based Web Services are becoming the XML based Web Services are becoming the norm on the Webnorm on the Web

Mobile devices using these web service Mobile devices using these web service are becoming increasingly popularare becoming increasingly popular

Mobile Devices use networks that are Mobile Devices use networks that are characterized by frequent disconnectionscharacterized by frequent disconnections

Web Service need to be universally Web Service need to be universally availableavailable

Need a solution that is transparently Need a solution that is transparently deployable and generally applicabledeployable and generally applicable

CachesCaches

Caches meets the requirements of Caches meets the requirements of being transparent deployment and being transparent deployment and general applicable general applicable

Caches are not a new idea, but XML Caches are not a new idea, but XML present a new set of challenges, due present a new set of challenges, due it vast set of operations and lack of it vast set of operations and lack of involvement in cachinginvolvement in caching

Solution is not complete !!!!Solution is not complete !!!!

System put forward by our friends System put forward by our friends at Microsoftat Microsoft

Build the XML cache into a HTTP proxy to Build the XML cache into a HTTP proxy to improve transparencyimprove transparency

In disconnected mode, when a request is In disconnected mode, when a request is received return its cached responses.received return its cached responses.

If no response is cached, client timeouts If no response is cached, client timeouts and save the request in write back queue and save the request in write back queue for later replay.for later replay.

Good idea, but has some inherent flawsGood idea, but has some inherent flaws

Issues in caching XML for Web-Issues in caching XML for Web-ServicesServices

Caching XML web services does increase Caching XML web services does increase the availability of the servicethe availability of the service

However, the availability of the web However, the availability of the web service is limited due to several issuesservice is limited due to several issues

Providing solutions to these issues will Providing solutions to these issues will greatly increase the effectiveness and greatly increase the effectiveness and efficiency of the cache and thus the efficiency of the cache and thus the availability of the web service during availability of the web service during periods of disconnectionperiods of disconnection

IssuesIssues

ConsistencyConsistency Understanding request and response Understanding request and response

messagesmessages User ExperienceUser Experience

ConsistencyConsistency

When operating in disconnected mode, When operating in disconnected mode, strong consistency is not possiblestrong consistency is not possible

But local (weak) consistency isBut local (weak) consistency is Providing weak consistency involves Providing weak consistency involves

understanding the interdependencies understanding the interdependencies between operation (difficult!)between operation (difficult!)

GOAL: A smart cache manager that can GOAL: A smart cache manager that can invalidate and/or transform earlier invalidate and/or transform earlier requests requests

User XPUser XP

Ideally, users should have the same Ideally, users should have the same experience when disconnected as experience when disconnected as when they are connectedwhen they are connected

High Availability Low

Weak Consistency Strong

Compromised User XP uncompromised

User XP: Cache Aware ClientsUser XP: Cache Aware Clients

Adding optional attributes to SOAP Adding optional attributes to SOAP messages for messages for cache awarecache aware clients clients allowing them to react, notifying allowing them to react, notifying users of possible uncertainties…users of possible uncertainties…

These attributes can be ignored by These attributes can be ignored by cache cache unaware clientsunaware clients

Thus the systems remains Web-Thus the systems remains Web-Service independentService independent

Understanding SOAP MessagesUnderstanding SOAP Messages

Despite Std protocols, web service Despite Std protocols, web service messages deviate considerably in messages deviate considerably in structurestructure

Using WSDL correctly formatted Using WSDL correctly formatted responses can be fabricated responses can be fabricated but but not not populated with default values populated with default values

Therefore there is a need to extend the Therefore there is a need to extend the WSDL specs to allow the cache/proxy to WSDL specs to allow the cache/proxy to be aware of the web-service semanticsbe aware of the web-service semantics

This can be done without effecting This can be done without effecting current implementations of Web Servicescurrent implementations of Web Services

Work AllocationWork Allocation

In essence, the core of the project In essence, the core of the project determines to specify extensions to determines to specify extensions to WSDL specificationsWSDL specifications

Darryl will focus on WSDL extensions Darryl will focus on WSDL extensions which attempt to under the which attempt to under the semantics of SOAP messagessemantics of SOAP messages

Justin will focus on WSDL extensions Justin will focus on WSDL extensions which determine interdependencies which determine interdependencies of SOAP messagesof SOAP messages