6.1.1 Global data bases
In this context we mean with global data base a permanent
(but still dynamic) data base in an organisation we are
dealing with. Taking aerial triangulation as an example,
essential information includes calibration data of camera
and files of control point data.
Complete integration between the global data base system
and the application software might be hindered by technical
and operational obstacles, especially when the integration
is desired to be done for a portable application software.
Firstly, the data input/output interfaces of the
application software has to be adapted to the corresponding
ones of the data base system. In worst case, if the data
base schema of the pertinent data does not follow the
structure assumed in the program, massive reprogramming is
required to convert the data to the required format. If
some commercial data base system is used, difficulties are
even likely, as observed by Elassal (1985). This is due to
the fact that commercial data base systems are usually not
well suited for dealing with numerical data. Question of
efficiency is also important, especially in those parts of
the application program where data base is used
extensively. If the data base system does not support
desired access methods well, then efficiency is poor. This
can be due to required conversions or complicated access
paths.
Secondly, the operational aspects have to be solved. If we
work within a multi-person organisation, it is likely that
somebody wants to alter data in the data base while an
application program is running. If not properly treated,
these alterations can have catastrophical consequences on
the integrity of the internal data of the program.
How should we solve these problems? A simple solution is to
restrict the access of the application program to the
global data base. This can be achieved by using front/back
ends that load the required data from the global data base
to an independent run-time data base. At the end of the
session reverse operations are performed.
This approach offers some obvious advantages:
- the application data base can be designed to fullfil
all the special requirements of the application
- the application program is working with a static
environment and consistency problems are avoided on
application level
- application program is well portable, only the
front/back-end modules have to be adapted for the
environment
However, there are also disadvantages. Firstly, the
consistency problem now occurs between the global data base
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