Integration of Legacy, Cots, And Map Data
Initial Replacement of Maps, Subsequent "Cut-over" of Legacy Svstem
As stated above, the replacement of legacy and map data with a single geospatial database is not
an uncommon model. In some cases, however, it is not possible to achieve simultaneous
replacement of the datasets. One approach to addressing such a situation is to continue to
operate and maintain the legacy system during the database construction process, and execute a
"cut-over" to use of the newly constructed geospatial system on a predetermined date, probably
shortly after database construction is completed.
Replace Maps. Retain Legacy System, Establish "Real-time" Interface
A third approach to database integration is to implement the geospatial system with the objective
of replacing the map system, but to retain the legacy system. If, however, the fimctionality of the
either system is dependent on access to data resident in the other, a high-level of data
compatibility and an interface between the systems will be required. If the functionality of the
system further depends on access to absolutely current data resident within the other system, then
the interface will need to provide "real-time" access to the other database.
Replace Maps, Retain Legacy System, Establish "Re~ort-tYpe" Interface
A somewhat less aggressive approach to interface implementation, which is viable in situations
where system functionality does not demand access to completely current data from the other
system, is a "report-type" interface. In this scenario, database content, or database transactions,
are periodically reported to the other system.
Load COTS Data to Geospatial Database with. or without, Modification
As with legacy data, COTS data can be integrated with map data via loading both data sets to the
same geospatial database. A further option, which has significant data maintenance
ramifications, relates to the modification of the COTS data or use of it "as is".
Load COTS Data to a Separate Database, Establish Interface
As with legacy data, the alternative model for COTS database integration is to load the data to a
database which is separate from the main geospatial database while facilitating data access
through establishment of an interface. In such a situation, the interface is likely to require "readonly"
functionality.
Understanding Integration Issues
As previously stated, within the context of a geospatial system, there are several models for the
integration of legacy and COTS data with map data. The following subsections discuss the
issues associated with integrating legacy and COTS data during geospatial database construction.
Legacy Systems
There are a number of issues which should be taken into account when considering the
integration of legacy and map data within a geospatial system. While these descriptions are
generic in nature, the concepts are broadly, perhaps universally, applicable. Examination of
these issues is an essential component of a credible data integration requirements analysis.
Further, the results of the analysis of these issues will be a valuable asset during the design and
accomplishment of the data integration process.
Data Synchronization
While determining how legacy data will be integrated into a GIS, one must determine the
processes associated with updating separate map and legacy systems. Typically the
disparate data sets are out-of-sync because they have each been updated through separate,
perhaps independent, processes within the enterprise.
Data/Source Freezing
During construction of a GIS database, it is required that sources, whether legacy or map,
be frozen. Freezing of data sources results in a stable source for use in database
construction. During these freeze times, daily operations of the enterprise must proceed
without hindrance. Therefore, special processes must be utilized to allow some manner
of update of the source data systems while protecting the stability of the frozen data
sources. Addressing this conflict of needs often requires copying or archiving of source
data, special capture of data changes, and the updating the geospatial database with
backlog data once the database construction has been completed.
Integration Match-Keys
In order to successfully integrate legacy and map data, feature-level match-keys are
required. Existing information such as ID numbers, grid references, coordinates, street
names and addresses are all potential match-keys which can be used to link map and
legacy data.
If no match-keys exist, a process of assigning match-keys maybe required. This can
either be performed prior to database construction, or as part of the database construction
methodology.
