Database Reference
In-Depth Information
to the CPSP engine, the engine first delivers all publications that have been
matched to their active subscriptions while they were disconnected.
Publish.
The CPSP engine stores all received subscriptions through
subscribe
requests to a list of active subscriptions. When an MB receives a
publish
message
from a mobile ICO (denoted as MIO in the following figures), it forwards the
message to the CPSP engine only if it has previously received a matching sub-
scription from the CPSP engine. Otherwise, the MB retains the publication since
no one is obviously interested. The MB stores all subscriptions received from the
cloud broker and local subscribers in a list of active subscriptions. Each publish
event from an MIO is subsequently matched to the list of stored subscriptions.
The matching process identifies whether a publication should be forwarded to
the CPSP engine or not which in turn performs its matching to the subscription
forest. A sequence diagram depicting the delivery of a new publication to an
interested subscriber is shown in Fig.
2
.
Announce.
Figure
3
shows the sequence of events following a new
announce
message. When an MB receives a new external data source announcement from
one of its MIOs, it announces a new publisher to the CPSP engine by sending the
corresponding announce message. The CPSP engine then stores the announce-
ment in a list of stored announcements and compares it with the list of stored
active subscriptions. If there are interested subscribers with subscriptions match-
ing the announcement, it may activate the publisher by forwarding the matching
subscriptions to the MB in the corresponding subscribe message. Any publisher
connected to an MB can
revoke
its previous announcement. When this happens,
the CPSP engine just needs to delete the announcement from its list of stored
announcements and unsubscribe messages to corresponding MBs. The revoke
Fig. 2.
Delivery of a new publication
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