Advanced Queuing - Oracle

Recipient
Elements of Advanced Queuing
The name of the agent may be the name of the application or a name assigned
by the application. A queue may itself be an agent—enqueuing or dequeuing
from another queue.
The address field is a character field of up to 1024 bytes that is interpreted in the
context of the protocol. For instance, the default value for the protocol is 0,
signifying a database link addressing. In this case, the address for this protocol
is of the form
queue_name@dblink
where queue_name is of the form [schema.]queue and dblink may either
be a fully qualified database link name or the database link name without the
domain name.
The recipient of a message may be specified by its name only, in which case the
recipient must dequeue the message from the queue in which the message was
enqueued. The recipient may be specified by name and an address with a protocol
value of 0. The address should be the name of another queue in the same database
or another Oracle database (identified by the database link) in which case the
message is propagated to the specified queue and can be dequeued by a consumer
with the specified name. If the recipient's name is NULL, the message is propagated
to the specified queue in the address and can be dequeued by the subscribers of the
queue specified in the address. If the protocol field is nonzero, the name and
address are not interpreted by the system and the message can be dequeued by a
special consumer (refer to "Third-Party Support" on page 1-21).
Recipient and Subscription Lists
Multiple consumers can consume a single message:
The enqueuer can explicitly specify the consumers who may retrieve the
message as recipients of the message. A recipient is an agent identified by a
name, address, and protocol.
A queue administrator can specify a default list of recipients who can
retrieve messages from a queue. The recipients specified in the default list
are known as subscribers. If a message is enqueued without specifying the
recipients, the message is sent to all the subscribers.
Different queues can have different subscribers, and the same recipient can be a
subscriber to more than one queue. Further, specific messages in a queue can be
Introduction to Oracle Advanced Queuing 1-23