In the contingent requests pattern, a participant sends a request to another
participant. If this participant does not answer within a given time, the request
is sent to a second participant. Again, if no response comes back, a third
participant is contacted, and so on. Delayed responses, i.e., responses arriving
after the time-out has already occurred, might or might not be discarded. If this employee does not accept the task on time, it is delegated
to another employee, and so on.
Atomic Multicast Notification
The atomic multicast notification pattern is explained as follows. A participant
sends out notifications to several other participants who have to accept the
notification. In specific cases, only one participant is required to accept it;
in other cases, a subset of the participants or all participants are required to
Imagine a production scenario with just-in-time delivery of some of the
components while the remaining components are kept in stock. Sometimes,
some of the components are not delivered on time.
In order to avoid getting components out of different warehouses and piling
them in front of the production facilities, the availability of all needed
components is checked. Only if all of them are available are the components
ordered to the production facilities.
Request With Referral
The request with referral pattern is especially important in service-oriented
environments where a registry is in place that allows binding to services at run
time. But also simple types of dynamic behaviour can be represented by this
pattern, for instance, the transmission of a new collaboration partner during
an interaction. In particular, the request with referral pattern can be used if a participant
A sends a message to another participant B containing a reference to participant
C. Although B does not need to know C in advance, B can now interact
with C. This pattern describes the concept of link passing mobility. As an example of this pattern, consider a customer who buys a set of books
online. The bookstore redirects the customer’s Web browser to the Web page
of an external payment service. Conceptually, this means that the bookstore
refers the payment service to the customer, who can then use the service,
although the customer was not aware about this service beforehand.
The relayed request pattern is common in emailing collaboration scenarios.
A participant A sends a request to another participant B who forwards it to
a third participant C who will actually interact with A. However, B always
gets copies of the messages exchanged in order to be able to observe the
conversation. As part of
a quality management program in the company and for legal reasons, all interactions
between the payroll services provider and the employees are being