UNIT 22 - THE OBJECT/LAYER DEBATE

UNIT 22 - THE OBJECT/LAYER DEBATE

  • A. INTRODUCTION
  • B. THE LAYER VIEW
  • C. THE OBJECT VIEW
  • D. COUNTER-ARGUMENTS FOR THE LAYER VIEW
  • E. AREAS OF APPLICATION
  • F. EXCEPTIONS
  • G. CONVERSION
  • REFERENCES
  • EXAM AND DISCUSSION QUESTIONS
  • NOTES

    This unit provides background on the debate about "object-oriented databases" currently raging in the GIS community. While this is often seen as complex technical topic, useful insights can be gained from exploring some of the underlying issues.

    UNIT 22 - THE OBJECT/LAYER DEBATE

    A. INTRODUCTION

    B. THE LAYER VIEW

    Data models

    C. THE OBJECT VIEW

    Scale

    Time

    Object orientation

    Identity

    Inheritance

    Encapsulation

    D. COUNTER-ARGUMENTS FOR THE LAYER VIEW

    Do objects really exist?

    Environmental modeling

    Gradients

    Enlightenment

    E. AREAS OF APPLICATION

    Resource management (layer view)

    Utilities (object view)

    Transportation, hydrology (mixed)

    F. EXCEPTIONS

    Transport networks

    G. CONVERSION

    REFERENCES

    Egenhofer, M. and A.U. Frank, 1987. "Object oriented databases: database requirements for GIS," Proceedings International Geographic Information Systems Symposium: The Research Agenda 2:189-211.

    Gahegan, M.N. and S. Roberts, 1988. "An intelligent, object- oriented geographical information system," International Journal of Geographical Information Systems Vol 2:101-10.

    Goodchild, M.F., 1989. "Modeling error in objects and fields," in M.F. Goodchild and S. Gopal, editors, Accuracy of Spatial Databases, Taylor and Francis, New York, 107-13. An accuracy perspective on the layer/object debate.

    Herring, J.R., 1987. "TIGRIS: topologically integrated geographic information system," Proceedings, AutoCarto 8:282-91.

    Herring, J.R., 1989. "A fully integrated geographic information system," Proceedings, AutoCarto 9:828-37.

    Maguire, D.J., M.F. Worboys and H.M. Hearnshaw, 1990. "An introduction to object-oriented GIS," Mapping Awareness 4(2):36-39. A good general introduction to the object oriented GIS.

    Worboys, M.F., H.M. Hearnshaw and D.J. Maguire, 1990. "Object-oriented data modeling for spatial databases". International Journal of Geographical Information Systems.

    EXAM AND DISCUSSION QUESTIONS

    1. It has been said that geographical data is special because it is inherently infinite - the world contains an infinite number of variables defined at an infinite number of places. Do you agree? Are there any other examples?

    2. Consider a set of driving directions from your house to your supermarket. Do they imply a layer or an object view of the world, or is neither appropriate?

    3. Which layers would you identify as most important in describing the natural environment?


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