The Query Service Set allows users to access the address space without browsing and without knowledge of the logical schema used for internal storage of the data.
Querying allows Clients to select a subset of the Nodes in a View based on some Client-provided filter criteria. The Nodes selected from the View by the query statement are called a result set.
Servers may find it difficult to process queries that require access to runtime data, such as device data, that involves resource intensive operations or significant delays. In these cases, the Server may find it necessary to reject the query.