1. Collaboration and Web Services
Geoffrey Fox
Professor of Computer Science, Informatics, Physics
and Director PTLIU Laboratory for Community Grids
Indiana University, Bloomington IN
2/5/2019
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2. Collaborative Web Services
First note that there are two distinct concepts
Collaboration as a Web Service
Such as “Audio-Video Conferencing” as a Web Service or “Text Chat as a Web Service”
Collaborative Web Services
Here we view a Web Service as specifying a (distributed) object and wish to share an object
Object could be a Web page, a Job status form, a scientific visualization, a PowerPoint slide etc. (not all of these are Web Services but all should be)
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3. Why Web Services for Collaboration
Well everything is meant to be a Web Service but also:
Web Services are MUCH EASIER to make collaborative than other objects because all input and output is defined by uniform XML messages
You need to teach your message service about collaboration!
Note local applications are NOT Web Services – input is things like “user mouse click” represented by “method events” (UI program interrupts) not “XML message events”
The elegance of collaborative web services suggest that it could be easiest to make object X (such as PowerPoint or SVG) collaborative not by traditional direct methods but by converting to a Web Service
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4. Types of Collaboration I
Shared Display: here one shares the rendering of a Web Service. No modification is needed of the web service. Rather this is handled by the portal controlling the user interface
Collaborative Replicated Web Services: here one replicates several instances of a web service and the task is to keep these copies consistent. This synchronizes inputs to multiple Web Services
Collaborative Web Service Access: here one has multiple clients accessing a single instance of a web service and obtaining consistent views. This multicasts output of a single Web service to multiple clients
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5. Types of Collaboration II
Shared Export is built on synchronizing the viewers (PDF HTML SVG Browsers) of standard formats. It differs from Shared Web Services in that user inputs (mouse clicks, keyboard) and not (XML Web service) messages are shared
One can share export with either a single or replicated back-end engine
The most elegant shared export models are built around viewers of documents sharing W3C DOM
It would be interesting to convert W3C DOM to a Web Service
Shared event is like shared Web service but is a custom “implementation” for each application
One can often choose between sharing user inputs or sharing implied change in specification of object state
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6. Collaboration: Shared Display
Sharing can be done at any point on “object” pipeline
Shared Display
Shared Web Service
Shared Event
Shared Export
Object
Object’
Object’’
Object Display
Object Viewer
Master
Event (Message) Service
Object Display
Shared Display shares
framebuffer with events corresponding to changed pixels in master client.
In these and following diagrams, we have three collaborating clients; is master while and are non-masters
Object Display
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7. Collaboration: Shared Export I
Another point on object to display pipeline
Shared Display
Shared Web Service
Shared Event
Shared Export
Driving Appl.
Object Display
Object Viewer
Object
Object’
Master
Shared Export shares
client side viewer with
events corresponding to
user interactions or information from driving application
Event (Message) Service
Object Viewer
Object Display
Object Viewer
Object Display
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8. Collaborative Web Service Access
Web Service either supports collaboration directly or uses event service
Web Service Interceptor Providing General Services
Set Collaboration Mode
Master
Web Service
Object Display
Object Viewer
Object
Object Viewer
Object Display
Web Service has a port on which collaborative modes set Web Service can be “front-end” (in middle tier) to complex back-end object
Event (Message) Service
Object Viewer
Object Display
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9. Web Service Interceptor
Collaborative Web Services are implemented “just” by replicating the messages that are output by the Web service
This replication is provided by the event service which needs both client and service dependent information
The service specific message function is provided by an interceptor or an adaptor which takes care of issues like security, collaboration, management, service information, which message service to use
The client specific function specifies the client profile telling event service how to filter events for each client
Depending on system implementation, the interceptor is either built into web service or a wrapper provided by event service
The latter implies that all messages between clients and (all) web services are handled by event service
There are ports on the interceptor allowing specification of Collaboration Session and giving event service access to information needed for appropriate filtered (as per profile) message delivery to clients
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10. Collaborative Web Service Access
This shows how the “Collaboration Web service” supports collaborative web services
Web Service Interceptor Providing General Services
Collaboration as a Web Service
Collaborative Web Service
Set Collaboration and Message Mode
Master Client
Web Service has a port on which collaborative modes set Web Service can be “front-end” (in middle tier) to complex back-end object
Event (Message) Service
Client
Client
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11. Collaborative Replicated Web Services I
This uses event multicast to support replicated web services
Web Service Interceptor Providing General Services
Set Collaboration Mode
Web Service
Master
Object Display
Object Viewer
Object
Web Service
Object Viewer
Object Display
Event (Message) Service
Web Service
Object Viewer
Object Display
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12. Collaborative Replicated Web Services II
The event service now replicates the messages INPUT to the master web service (In Collaborative Web Service Access we replicated messages OUTPUT to the client)
Again we use a special “collaboration” port on the Web Service to set up links between clients
Note publish/subscribe mechanism in the events service supports the late joiners (in other collaboration models as well)
The event service can also handle messages between Web services and clients and provide the user customization service but this is not shown on previous foil
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13. Collaboration: Shared Export II
One can use replicated “driver” for shared export
Shared Display
Shared Web Service
Shared Event
Shared Export
Driving Appl.
Object Display
Object Viewer
Object
Object’
Master
Event (Message) Service
Driving Appl.
Object Viewer
Object Display
Driving Appl.
Object Viewer
Object Display
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14. Collaboration: Shared Event I
Object must be changed in object (application) specific fashion
Master
Shared Event shares State change events
Object
Object’’
Object Display
Event (Message) Service
Object
Object’’
Object Display
Object
Object’’
Object Display
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15. Collaboration: Shared Event II
Object events can be shared at any point in pipeline
Master
Shared Event shares State change events
Object
Object’’
Object Display
Event (Message) Service
Object Display
Object’’
Object Display
Object’’
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16. CollabWS: Collaboration as a Web Service
This includes Audio-Video conferencing, Instant Messengers, shared applications and tools
There are basic standards H323 and SIP
There are peer to peer collaboration approaches like JXTA from Sun
There are various commercial products – Groove Networks effectively defines some shared application interfaces
CollabWS defines a superset of collaboration properties and subservices in XML/WSDL
Then you provide several bindings of collabws.wsdl to new transports and old ones (binary H323)
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17. H323 SIP JXTA
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18. SIP H323 JXTA
SIP
H323
JXTA
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19. A Typical SIP Message
REGISTER sip:registrar.biloxi.com Via: SIP/2.0/UDP :5060 To: Bob From: Bob Call-ID: CSeq: 1826 REGISTER Contact: Expires: 7200 Contact-Length: 0
Initially build a wrapper that accepts such messages and converts to …..
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20. Collaboration as a Web service - now
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21. SIP as XML
<sipasxml> <register> sip:registrar.biloxi.com</register> <via> SIP/2.0/UDP :5060</via> <to> Bob </to> <from tag="456248" > Bob </from> <call-id> </call-id> <cseq> 1826 REGISTER </cseq> <contact> </contact> <expires> 7200 </expires> <contact-length> 0 </contact-length> </sipasxml>
So this is either an internal format to which we map SIP messages or it is an external format used for Collaboration Web Service
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22. Future Collaboration Web Service
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23. Messaging/Events as a Web Service
We can implement messaging subsystem (between WSDL resources) with either direct messages or by a queued system where you publish messages to queues and subscribe as receiver to particular queues
There are many different publish/subscribe models
JMS is a cluster of central servers
JXTA is a very dynamic Peer to Peer model where pipes are queues and topics (metadata) are service advertisements
Implement JMS API with JXTA protocol – different WSDL bindings here have different fault tolerance/reliability semantics
Could use JMS as long distance “carrier” between JXTA peers
JXTA provides higher performance than JMS for nearby recipients
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24. Destination Source Matching
Event Web Service
Web Service 1
(Virtual) Queue
Web Service 2
Destination Source Matching
Filter
Routing
workflow
WSDL Ports
Filter is mapping to PDA or slow communication channel (universal access) – see our PDA adaptor
Workflow natural as all messages “intercepted” by Event Web Service
Routing illustrated by JXTA
Destination-Source matching illustrated by JMS
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25. Broker Network Software multicast P2P: Brokers are clients Broker
Resource
Data
base
Broker
Broker
Broker
Broker
Broker
Broker
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26. Narada JXTA/JMS Integration
Is a network of event brokers which can reliably deliver XML specified events
Using openJMS selection module, becomes a distributed or conventional Java Message Service
Linking special JXTA proxies, it can link JXTA communities
Think of JXTA JMS and Narada as different bindings to event/messaging web service
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