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Alternatively, the console may wish to interact with a set of agents, possibly all of them. In this case, the console establishes a set of criteria in the form of a query (i.e. "all printers where vendor == 'HP'") and builds a list of available agents. In this case, the console sends a multicast query (using a topic exchange) and collects responses from matching agents. Furthermore, if a new agent comes on line that meets the criteria, the console will learn about the new agent.

Query

A query is initiated by a console and answered by one or more agents. A query requests data from an agent and supplies selection criteria for the data. Once each agent sends the requested data to the console, the query operation is complete.

Subscription Query

A subscription query is similar to a normal query except that after the requested data is sent by an agent, the query remains open and subsequent changes to the requested data are sent to the address supplied by the console.

A subscription query is kept open by the agent and is closed in one of two situations. Either the console explicitly closes the subscription query or it times out after a time interval. The console may periodically refresh an exiting subscription query to keep it from timing out. This allows for subscription queries to be cleaned up in case the requesting console goes away without shutting down the subscription.

Schema Query

Method Invocation

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