Information Technology Reference
In-Depth Information
“Metadata”
Extractor
Controller
Scanner
“Metadata”
Representation
Editor
Repository
Manager
Fig. 17.12
The Component diagram of PreScan
rescanning services that do not start from scratch but exploit the previous status of
the index, and (e) associate the extracted “metadata” with other sources of knowl-
edge (i.e. registries of Representation Information). Figure
17.12
shows the overall
architecture of PreScan.
17.5 Preservation Orchestration Manager
Preservation is not a static activity, but an evolving process which involves per-
sons and systems. They react in response to evolving conditions (i.e. change
events) which could impact on long-term preservation of the digital content infor-
mation. So, it is important for a digital archive to monitor, notify and alert (in
order to synchronise) any evolving condition and entity within the preservation
environment.
The CASPAR Preservation Orchestration Management provides notification
and alert service within the CASPAR Preservation Infrastructure. The CASPAR
Preservation Orchestration Manager (POM) component is an implementation of the
Publish-Subscribe pattern. The Publisher-Subscriber design pattern helps to keep
the state of cooperating entities synchronized. To achieve this it enables one-way
propagation of changes: one publisher notifies any number of subscribers about
changes to its state.
In the proposed solution, one component takes the role of the publisher and all
components/entities dependent on changes in the publisher are its subscribers. In
the CASPAR preservation environment we can say that any information change
(such as a gap in the Representation Information, a file format change, etc.) can be
viewed as a state change about which the Data Holder can declare an interest to be
notified.
The components involved in the role of Data Preserver have the responsibility to
publish notification messages in order to alert the interested Data Holder. Both Data
Preserver and Data Holder can be humans or software components.
