General Information on Sequences 

Implementation off Web Services Reliable Messaging ensures that messages are transmitted with the help of logical sequences (or SOAP sequences) from the user of a service to the provider. A logical sequence is implemented using a technical sequence. This is based on the WS-RM protocol, and it contains one or several messages and a queue.

Sequences contain a unique identifier. Messages in a sequence are numbered consecutively. The WSRM sequence header in the SOAP message identifies the sequence to which a message belongs.

WS Reliable Messaging implementations at the sender and receiver sides ensure that messages are transferred securely. A prerequisite for this is that incoming messages are confirmed by the receiver. For this, the specification defines the format of an acknowledgement that the receiver sends to the sender as confirmation. The sender waits for the confirmation and, if necessary, keeps sending the message until the confirmation is received.

To avoid unnecessary network communication, the receiver does not have to confirm the receipt of every single message individually, but can confirm whole (not necessarily related) sections in one acknowledgement - for example, confirm that messages 1, 3, and 5 have been correctly received.

Since messages 2 and 4 were not confirmed, they are sent again. The sequence is only finished when successful receipt of these messages, too, has been confirmed.

Errors during the transfer of a sequence can pertain to the sequence or to the message. When a sequence is created, a remote message call is executed first. This uses the same configuration settings as the first message that was sent using the sequence. If the message call terminates with an error (for example, Login not possible or Configuration missing on provider side), the cause of the error is displayed. As soon as the cause of the error has been resolved (for example, it has been configured correctly), the sequence can be restarted using the Sequence Monitor. If an error relates to a message, the cause of the error can also be displayed in the Sequence Monitor. The message key, the message status, and the user name that was used to transmit the message are displayed.

For more information, refer to the section Analyzing a Sequence.