Semantic Interoperability Issues in the Geosciences

Mark Gahegan
Geographic Information Science
Curtin University of Technology
PO BOX U 1987
Perth 6001, WESTERN AUSTRALIA
phone: +618 9266 3309
fax: +618 9266 2819
E-mail: mark@cs.curtin.edu.au
Web: http://www.cs.curtin.edu.au/~mark/
 
 

Over the recent past, considerable progress has been made towards interoperability between mainstream GIS packages. However, the interoperability issues addressed so far have been largely restricted to a class of GIS using two-dimensions and where the geographic models considered (the conceptual basis of the systems) are quite similar. Within the whole range of the geosciences there are many other types of systems, some devoted to remote sensing, others to the modelling of true three dimensional geological structure. Each have their own idiosyncrasies in terms of conceptual model, data structures and functionality. It is my aim with this position paper to bring into the mainstream some of the issues concerning this wider set of packages, particularly with regard to the needs of the remote sensing and exploration / mining communities of users, whose needs have perhaps been addressed less rigorously than they would like.

Support for a broader range of geoscientific information systems

Of key importance to the strategic development of open systems are the embracing of the three (and four) dimensional concepts that are available in many geologically oriented systems, including those used for exploration, mining and groundwater modelling. Examples of commercial systems are Surpac 2000, Vulcan and Micromine, although there are many more. The users of these systems represent a very large community whose data translation and interoperability needs are often overlooked. In many respects, interoperability within these systems is just as pressing an issue as with traditional GIS. The systems are extremely diverse with respect to function and role. For example, many exploration companies will ordinarily use two, three, or more completely distinct systems at the same time, to fulfil all their planning and modelling needs (e.g. minesite layout, drill-hole logging, mineral potential mapping). The costs involved in moving data between these systems are enormous, with some companies having to settle for essentially re-entering the data each time it is required in a different system. Consequently, there is a huge potential for improvement, which interoperability could satisfy, and a commitment within many organisations to solve these issues once and for all. Whilst the OGIS reference model appears up to the task, extensions to the OGIS Geodata Model are required to fully support three dimensional objects, or objects with coordinates in the vertical plane such as geological profiles, faults, dykes and drill-holes. Existing packages often operate within a quite restricted semantic framework; the same logical entities being precisely and similarly defined (as far as the user is concerned) across many systems. Some standards exist for nomenclature and meaning, such as defined by the Australian Minerals Industries Research Association (AMIRA) sponsored GEODATA project. Any planned interoperability must embrace the significant progress that has already been made in defining the logical entities in use across existing systems since these are becoming the accepted norm.

Support for remote sensing and image processing systems

Also of critical importance is the need for further progress to better integrate remote sensing activities with GIS. The recent OGF initiative on image formats and meta-data lays a foundation for better integration, but falls short in respect of the mechanisms by which the geographic objects used in GIS are formed from image data. This in turn raises two related issues: the choice of object formation strategies (image segmentation) by which the objects used by GIS are made, and the semantic definition of geographic objects so that their meaning is communicable in some manner. Image segmentation is problematic to describe formally; the algorithms, data and knowledge used will, in effect, determine the objects formed. So, object semantics are partly determined by the abstraction (extraction) processes applied. (Smith et al., 1992; Gahegan & Flack, 1996; 1997). Alternatively, object semantics may be defined in linguistic or high level terms as shown by Kuhn (1994). It is necessary to ensure that the meaning of data can be communicated along with the data itself, since without a clear statement of the meaning the opportunities for data misuse increase. Both of the above approaches may be required, depending on the origins of the data. If a statement of meaning can be formalised then it is possible to include some software safeguards as part of interoperation functionality. Further details of my research in this area can be found in the accompanying conference abstract and in earlier work (e.g. Gahegan, 1996).

Summary

In summary, my position is one of concern for object semantics in the wider realm of geo-information processing. I am keen to be involved in any initiatives to further develop the semantic basis for interoperability in order to improve the quality of data exchange, and the sharing of functionality between systems. I see this area as being one of the current shortcomings with the OGIS Geodata Model which could be successfully addressed as part of an ongoing collaboration. My relevant project experience (shown below) indicates how I am currently active in this area and involved with many industry representatives (both users and developers) from the larger realm of the geosciences..

References
Gahegan, M. N. (1996), Specifying the transformations within and between geographic data models. Transactions in GIS, Vol. 1, No. 2, pp. 137-152.

Gahegan, M. N. and Flack, J. C. (1996), A model to support the integration of image understanding techniques within a GIS. Photogrammetric Engineering and Remote Sensing, Vol. 62, No. 5, pp. 483-490.

Gahegan, M. N. and Flack, J. C. (1997). Recent developments towards integrating scene understanding within a geographic information system for agricultural applications. Submitted to Transactions in GIS (under review).

Kuhn, W. (1994), Defining semantics for spatial data transfers. Proc. 6th International Symposium on Spatial Data Handling, (Ed. Waugh, T. C. and Healey, R. G.), Edinburgh, Scotland, pp. 973-987.

Smith, T. R., Ramakrishnan, R. and Voisard, A. (1992), Object-based data model and deductive language for spatio-temporal database applications. In: Geographic Database Management Systems (Ed. Gambosi, G., Scholl, M. and Six, H.-W.), Springer Verlag, pp. 79-102.