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(a)
(b)
(c)
F
IG
. 2. Broadcast organization in
Broadcast Disks
. (a) Data base pages. (b) Distribution of data base
pages. (c) Distribution of data base pages.
Broadcast disks solve some very basic problems in the broadcasting of public
data but they have several limitations. Like flat broadcasting, they are intended to
broadcast all of the data items in the database. This is impractical, unrealistic, and
unnecessary. Since in reality, a single public data could satisfy a large number of
clients and all data items in a database are not of interest to the clients at the same
time. In addition, they assume the same granularity for the data items on air channel
and disk pages—if a data item is to be broadcast more frequently (replicated), then
the entire page has to be replicated. Moreover, due to the plain structural nature of
the page-based environment, the research looked at the pages as abstract entities
and was not meant to consider the contents of the pages (data and its semantics) as
a means to order the pages. In object-oriented systems, directed semantics among
objects greatly influence the method in which objects are retrieved, and thus, have
their direct impact on the ordering of these objects/pages. In addition, the replication
should be performed at the object-level granularity.
3.1.1.3 Hierarchical Broadcast.
The concept of the broadcast disks dis-
cussed in Section
3.1.2
was extended by Peng and Chen
[54]
to parallel broadcast
channels with different speeds. In addition, they used the access frequency of a data
item as a means to allocate the data item on a broadcast channel—hot data items
are allocated to the faster channel. Given a set of data items with different access
frequencies and several broadcast channels of different speed, the so called Variant-
Fanout with the constraint K (VF
K
) heuristically allocates data items to different
channels in order to minimize the average expected delay of all data items. Fig-
