Answer:   Within the publish-and-subscribe model, document processing is the process of evaluating documents against trigger conditions and executing the appropriate trigger services to act on those documents. The processing used by the Integration Server depends on the document storage type and the trigger settings. The Integration Server offers three types of document processing.

* At-least-once processing indicates that a trigger processes a document one or more times. The trigger might process duplicates of the document. The Integration Server provides at-least-once processing for guaranteed documents.



* At-most-once processing indicates that a trigger processes a document once or not at all. Once the trigger receives the document, processing is attempted but not guaranteed. The Integration Server provides at-most-once processing for volatile documents (which are neither redelivered nor acknowledged). The Integration Server might process multiple instances of a volatile document, but only if the document was published more than once.



* Exactly-once processing indicates that a trigger processes a document once and only once. The trigger does not process duplicates of the document. The Integration Server provides exactly-once processing for guaranteed documents received by triggers for which exactly-once properties are configured.



Note - At-least-once processing and exactly-once processing are types of guaranteed processing. In guaranteed processing, the Integration Server ensures that the trigger processes the document once it arrives in the trigger queue. The server provides guaranteed processing for documents with a guaranteed storage type.

The following section provides more information about how the Integration Server ensures exactly-once processing.



Note: Guaranteed document delivery and guaranteed document processing are not the same things. Guaranteed document delivery ensures that a document, once published, is delivered at least once to the subscribing triggers. Guaranteed document processing ensures that a trigger makes one or more attempts to process the document.