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Steve and Aron, Some time ago, in the GALEON framework we discussed about a WCS RFC to: 1) Enable Grid Computing support of Access Services; 2) Support of long time processing; 3) Support redirection and ?shared access?. In order to support this request, we prepared a discussion paper: I attached the draft document hoping it could be useful for the present discussion. Best, Stefano
Aaron: Good synopsis. I differ with your definitions but only very slightly. Here's my attempt at defining the terminology. But first: Putting a definition on the term ?asynchronous? without stating ?what? is asynchronous is pointless because it is too abstract. Its definition from answers.com is ?Lack of temporal concurrence; absence of synchronism? which is meaningless out of context. So what are WE talking about when discussing asynchronous - believe we mean ?asynchronous result to an OWS request?. Notice I didn't say asynchronous response. The reason is that I don't want to confuse the HTTP response (which is always synchronous) with the actual result from a request. In the past we used result and response interchangeably because they always coincided. Client: originator of a request. Server: handler of a request. There first two definitions (client and server) are here only to help clarify the next definitions since a client becomes a server when dealing with pushed
results.
Result: the data generated by a server due to a request from a client. This definition does not imply synchronous or asynchronous. Asynchronous result: a result made available at an indeterminate time after reception of an asynchronous request. This definition does not necessarily imply polling, pushing, or notification. Asynchronous request: a request which produces an asynchronous result. Polling: is a client actively sampling (using synchronous requests and responses) for the result status. Pushing: is where the transmission of something originates with the server. The client waits for the server to send it something. Notification: Let me define it as: a server pushing a result status to a client. Personally I see notification and push as being the same but I'm hearing others here say that notification does not actually send the asynchronous result but simply sends a simple result status stating that the result is ready. Pushed result: is where the asynchronous result is pushed by the server to the client. Result status: the current status of an asynchronous result: ready, completed, processing, not started, etc. Response: one of many possible messages when replying to a request. Synchronous response: a single message immediately returned by a server in response to a synchronous request. Acknowledgement: Synchronous response acknowledging reception of an asynchronous request. Persistent query: a client makes a query and marks it as ongoing or "persistent". When the conditions of the persistent part of the query are satisfied asynchronous result are generated. A simple example would be asking for temperature information for the area of Texas from yesterday to the end of next week. Whenever new temperature information became available to the server, it would be sent to the client or the client would be notified. When the server notices that the end of next week has arrived, it invalidates or discards the query. Cheers -- Steven Keens
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NotesOnAsynchronousAccessServices_v22.pdf
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