CONCLUSIONS
The techniques for data organization for interchange have progressed from
specific formats, individually-defined in paper documents through definition
of format families for similar data (LANDSAT CCT) to definitions of data
modules. Concurrently, the ISO has defined a layered approach to the
definition of the interchange process, which clarified the need for the
separation of the format definitions from the generic format descriptions,
ISO 8211 and the GDIL provide format descriptive approaches which may be
used to describe any of the format structures defined by the various
disciplines, allowing their data to be transferred between systems with a
minimum of human intervention or special logging programs.
LGSOWG experience has shown that the self-defining or descriptive approach
often fails to result in the generality intended by the designers of a
format. Typically, many users will implement one "instance" of the format
family, ignoring all the information describing the structure in general.
This is often the fastest, least expensive way in which to read the data
from one particular source. With this experience in mind, groups developing
nev standards will often shun the general formats (such as ISO 8211) because
they have too much overhead for any specific application.
ACKNOWLEDGEMENTS
Development of the GDIL has been sponsored by the Information Systems Office
of the (USA) National Aeronautics and Space Administration Office of Space
Science and Applications.
This report was partly written at the Jet Propulsion Laboratory, California
Institute of Technology, under contract to NASA.
The authors would like to acknowledge the efforts of all those engaged in
the arduous task of developing and promoting standards. It is generally a
thankless task, usually resulting in more criticism than praise. We would
also like to thank David Harris of PCI for his thoughtful comments and
editing of this paper.
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Billingsley, Fred C. (1985). General Data Interchange Language,
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Canadian Council on Surveying and Mapping (1984). National Standards for
the Exchange of Digital Topographic Data, Volume 1.
Canadian Council on Surveying and Mapping (1985). Proposed Standards for a
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EOSAT (1985). User's Guide for Landsat Thematic Mapper Computer-Compatible
Tapes, Earth Observation Satellite Company, Lanham, MD.
Goodenough, D.G., Palimaka, J.J., Dickinson, K., Murphy, J. (1979).
Standard Format for the Transfer of Geocoded Information in Spatial Data
Polygon Files. CCRS Research Report 79-3, Canadian Centre for Remote
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