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Materialized views, known as snapshots in
prior releases, are used to replicate data to non-master
sites in a replication environment. Updatable materialized
views enable users to maintain data at their local site (even
a mobile user with a laptop) and later resynchronize with
main site by applying the local changes to the master site
and retrieving the any changed data for the materialized view
site from the master site.
With Oracle9i Replication, you can create
multiple tiers, or levels, of materialized views. This
multitier capability offers greater flexibility in the design
of a replication environment. Multitier materialized
views are useful in a variety of situations, including:
- Branch Office configurations
- Sales Force Automation applications
- Indirect connectivity situations
Multitier materialized views are ideal for
organizations structured on three or more levels or in situations
constrained by network resources. As an example, in
the Corporate Headquarters(HQ), Regional Office, Branch Office
configuration in the picture above, the Branch office
has no direct network connectivity requirement to the Headquarters
site. Alternatively, mutlitier materialized views can
be configured to restrict the data available at each site.
For example, the replication environment can be configured
so that the Headquarters office maintains all of the data,
the Regional office maintains the data necessary to support
the customers in the particular region, and the Branch office
receives a further subset of the data from the Regional office
- only the information necessary to support the Branch office.
Similarly, another materialized view can be created from the
Branch Office to facilitate a salesperson's ability to view
and maintain information on individual customers even when
disconnected from the company network.
In a multiter updatable materialized view
configuration, you can create an updatable materialized view
based on another updatable materialized view. Each middle
tier updatable materialized view performs as a replication
master site for any subsequent updatable materialized views
and can refresh the data incrementally, ie, retrieve only
the changes since the last resynchronization with the master
site. Each materialized view that acts as a master
is known as a master materialized view, performing
conflict detection and resolution for any updates that come
from the subsequent materialized view sites. If a change
that originated from a lower level site (for example,
the Branch office in the picture above) is rejected,
the data values of the parent master materialized view
(the Regional Office) are refreshed to the lower-level site
(Branch Office) via the normal refresh mechanism. Changes
percolate up to the top-level sites by successive refreshes
of the intermediate level sites.
This capability is available in both the Standard
and Enterprise Edition of Oracle9i.
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