Does WCF allows me to change client data by running WCF service hosted in Server?

I  have ASP.NET application.
The client (aspx)  is analyzing  financial data  in order to make some very important decission.
It's very important to see always fresh data.
The point it that  while long work client  the data may be changed.
In our   application clent can know it when he is saving data (post back event)
Application  checks client data and data in Cash and says  to client , that  desiccation   could be wrong , cause  base data  were changed.
Application Cash is refreshed automatically by running WCF.
Is there some way to let all  WEB clients know that data are refreshed before they cal server ?
YampolkaValeriya YampolskaAsked:
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BuggyCoderCommented:
you need to use callbacks, but this works on TCP and other connection oriented bindings.
This way your client can implement the callback contract and service can call the callback method to tell the client that data has changed.

something like publish subscribe model, here is an example:-
http://msdn.microsoft.com/en-us/library/ms752254.aspx
http://www.codeproject.com/Articles/34333/Topic-based-publish-subscribe-design-pattern-imple
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tovvenkiCommented:
Hi,
I think you can create a duplex service and use it to contact the client.
See the following urls which might show you how it works and how to do it
http://weblogs.asp.net/dwahlin/archive/2008/06/16/pushing-data-to-a-silverlight-client-with-wcf-duplex-service-part-i.aspx

http://msdn.microsoft.com/en-us/library/cc645027(v=vs.95).aspx

I hope that this helps,

Thanks and regards,
Venki
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YampolkaValeriya YampolskaAuthor Commented:
I need  to have WEB client ( not windows client)

What we have :
1) we have all session ID in application cash  memory and associated URI  all our users , which teoretically are usingg our application

2) all .aspx net page have some hidden field , lets say isSomethingUpdated = false and Event _ onchange(isSomethingupdated) which occurs when  field  is changed

3)  when duplex woks   I will  know .

What I need  to send aynchronyously xmlHTTP request to all clesnts basing on SessionID
this  Request will update on the client siide all .aspx pages , making field  isSomethingupdated= true. In this case  Event _ onchange would be runnind.
can I do this? how?
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YampolkaValeriya YampolskaAuthor Commented:
The alternative of  Ajax polling could be "  Push HTTP :tech"   when client ( Browser ) connection is always "alive "( KeepAlive= true)
 Could somebody to tell  me how /when it's could be implemented  ?
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