Each of those commands must be issued individually. The user
is responsible for administering the names of input files and
output files. The example shows that the user has to provide
unique names for each intermediate result so that it can be cor-
rectly referenced in subsequent procedures. This task is a
common source of errors. Commonly, users create a processing
plan themselves to avoid loosing track.
Employing VGIS, the user only has to create the work flow
depicted in Figure 8 and to start its execution. While process-
ing the flow chart the user is then prompted by the system to
enter the rules for reclassification interactively. The result is
displayed on the screen.
7 FUTURE RESEARCH
VGIS does not yet include conditional and iteration operators
as they are used in formal programming languages. The 20
universal analytical GIS operations employed do not account
for any three-dimensional or temporal reasoning. The formali-
zation given in (Albrecht 1996) can only be a preliminary one
as the universal data model that underlies the definition of
operations is based on an older draft of OGF's geodata model
(OGF 1993) which has in the meantime been considerably al-
tered. Finally, it would be extremely useful if not only the
services-directed operations on the application level were stan-
dardized, but the low-level functions, that are actually used by
OGIS-conform systems, as well. Research into this direction is
currently pursued by the authors both within OGF and ISO's
technical committee 211 (Geoinformation).
8 LITERATURE
Albrecht, J., 1994. Universal Elementary GIS Tasks—Beyond
Low-Level Commands. In Proceedings of the 6th Symposium
of Spatial Data Handling, pp. 209-222, Edinburgh.
Albrecht, J. 1995. Semantic net of universal elementary GIS
functions. In Proceedings ACSM/ASPRS Annual Convention
and Exposition Technical Papers, Vol. 4 (Auto-Carto 12),
pp. 235-244.
Albrecht, J., 1996. Universal GIS Operations for Environ-
mental Modeling. Proceedings of the Third International
Conference/Workshop on Integrating GIS and Environmental
Modeling, Santa Fe, NM. Santa Barbara: National Center for
Geographic Information and Analysis (published as CD).
Albrecht, J., 1996. Universal Analytical GIS Operations. A
Task-Oriented Systemization of Data Structure-Independent
GIS Functionality Leading Towards a Geographic Modeling
Language. University of Vechta, ISPA: Mitteilungen 23,.
Aronoff, S., 1991. Geographic information systems: a
management perspective. Ottawa: WDL Publications.
Burrough, P., 1986. Principles of geographic information sys-
tems for land resources assessment. Oxford: Clarendon
Press.
Burrough, P., 1992. Development of intelligent geographical
information systems. In International Journal of Geographi-
cal Information Systems, 1, 1-11.
Chang, S., 1990. Principles of visual programming systems.
Englewood Cliffs: Prentice Hall.
Egenhofer, M. and A. Frank, 1992. Object-Oriented Modeling
for GIS. Urisa Journal 4(2):3-19.
Frank, A., 1993. The Use of GIS: the user interface is the sys-
tem. In Medyckyj-Scott, D. and H. Hearnshaw (Eds.) Human
Factors in Geographical Information Systems, pp. 11-12,
London: Belhaven Press.
Glinert, E., (Ed.), 1988. Visual programming environments.
Los Alamitos: IEEE Computer Society Press.
Goodchild, M., 1992a. Geographical information science. In
International Journal of Geographical Information Systems,
1, 31-46.
Goodchild, M., 1992b. Spatial analysis using GIS. 2°. Santa
Barbara: National Center for Geographic Information and
Analysis.
Hamilton, G. and M. Worboys, 1996. User Perspectives on
Geographic Space. Proceedings GISRUK ‘96, Canterbury:
University of Kent.
Kuhn, W. (1992): Paradigms of GIS Use. In: Proceedings 5th
International Symposium on Spatial Data Handling. Char-
leston, S.91-103.
Laurini, R. and D. Thompson, 1992. Fundamentals of spatial
information systems. London: Academic Press.
De Man, E., 1988. Establishing a geographic information sys-
tem in relation to its use. In International Journal of Geo-
graphical Information Systems, 3, 257.
Mark, D. and M. Gould, 1991. Interacting with Geographic In-
formation: a commentary. Photogrammetric Engineering &
Remote Sensing, 57:1427-1430.
Medyckyj-Scott, D. and H. Hearnshaw, 1993. Human Factors
in Geographical Information Systems. London: Belhaven
Press.
Monmonnier, M., 1989. Graphic scripts for the sequenced
visualization of geographic data. In Proceedings GIS/LIS'89,
pp. 381-389, Falls Church: ASPRS/ACSM.
OGF, 1993. The Open Geodata Interoperability Specification,
Version 1.0, preliminary draft, November 15, 1993. Open
GIS Foundation, Cambridge, MA.
Rhind, D., and N. Green, 1988. Design of a geographical in-
formation system for a heterogeneous scientific community.
In International Journal of Geographical Information Sys-
tems. 2, 175.
Schenkelaars, V., 1994. Query classification, a first step to-
wards a graphical interaction language. In Molenaar, M. and
S. de Hoop (Eds.) Advanced Geographic Data Modelling,
pp. 53-65.
Timpf, S. and A. Frank, 1995. À multi-scale DAG for carto-
graphic objects. In Proceedings ACSM/ASPRS Annual Con-
vention and Exposition Technical Papers, Vol. 4 (Auto-
Carto 12), pp. 157-163.
Tomlin, D., 1990. Geographic Information Systems and Car-
tographic Modeling. Englewood Cliffs: Prentice Hall.
Turk, A., 1992. GIS Cogency: cognitive ergonomics in geo-
graphic information systems. Unpublished dissertation. Mel-
bourne: Department of Surveying and Land Information,
University of Melbourne.
Unwin, D., 1990. A syllabus for teaching geographical infor-
mation systems. In International Journal of Geographical
Information Systems, 4, 461-462.
Voisard, A., 1995. Open GIS: A tool for environmental infor-
mation management. In Kremers, H. and W. Pillmann
(Eds.), Space and Time in Environmental Information Sys-
tems, 9th International Symposium on Computer Science for
Environmental Protection, pp. 160-167.
Yuan, M. and J. Albrecht, 1995, Structuring geographic infor-
mation and GIS operations. In Frank, A. and W. Kuhn (Eds.)
Spatial Information Theory: A Theoretical Basis for GIS,
pp. 107-122, Berlin: Springer.
88
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
KI