Coping with Topological and Directional Relations
Based on 3-Dimensional Geometric Representations
Peter Wazinski, Gerd Herzog,
SFB 314 - Project VITRA
Universität des Saarlandes
D-66041 Saarbrücken
Germany
Appeared in: Spatial Concepts: Connecting Cognitive Theories with Formal
Representations, Workshop Notes, 10th ECAI, Vienna, Austria, 1992.
In the VITRA (Visual Translator) project we are concerned with natural
language access to visual data. Our previous work on integrating
computer vision and natural language processing focused on
2-dimensional representations of the spatial environment. The aim
now is to generalize our former work in order to deal with
3-dimensional geometric scene representations.
Two main applications are under investigation:
- The automatic generation of incremental natural language route
descriptions taking into account the changing visual context
while following the route
- Natural language dialog with an autonomous mobile robot about
its spatial environment in order to control the positioning
of the robot system and its effectors
For both scenarios, a detailed 3-dimensional geometric representation
forms the starting point for the definition and representation of
spatial relations that in turn are used for the analysis and synthesis
of spatial reference expressions in natural language.
The theoretical framework of our research is the idea of two-level
semantics that originates in the work of Bierwisch
(Bierwisch (1983)).
The conceptual system functions as a representational mediator
for various cognitive subsystems such as the visual, auditory and -- of
course -- the linguistic system.
Within the linguistic system the meaning of a lexical item is
represented as a grammatically determined, item-specific formation of
certain parameters, the values of which are available on the
conceptual level.
Thus, the conceptual and the linguistic system are independent, and
conceptual knowledge is represented in a language-independent way.
For directional prepositions and dimensional adjectives this approach was
elaborated in Lang (1991) and Lang et al. (1991).
Herweg (Herweg (1989)) used the same theoretical basis for topological
prepositions.
Both, Lang's and Herweg's approaches to spatial expressions
are purely qualitive. Quantitative aspects like the distance
evaluation between the reference object and the object to be located
or linguistic hedges (``X is fairly behind Y.'') are not taken
into account. For these quantitative aspects of spatial descriptions
we intend to adopt our own work on applicability degrees
(Herzog et al. (1990), Wazinski (1992)).
The mathematical basis for Herweg's approach to topological
prepositions is algebraic topoplogy.
Within the context of geographic information systems Egenhofer
has devoloped a more elaborate method that also relies on algebraic
topology and provides the formal definition of (binary) topological
relations as well as an inference mechanism for these relations
(c.f. Egenhofer (1991)).
Although we assume that fairly complete 3-dimensional geometrical
representations of the domain under discussion will be available
the task of reasoning about spatial information can not be neglected:
- In order to generate adequate spatial reference expressions in
a natural language dialog one has to anticipate the inferences
the dialog partner will draw based on a given spatial description.
In addition to pictorial reasoning methods (c.f. Schirra (1989))
we also intend to incorporate propositional spatial reasoning techniques.
- Real world applications have to cope with the dynamic nature of
the environment.
Since there are other agents acting within the scene known objects
may change their location or previously unknown objects
occur.
Spatial reasoning will be required in order to deal with the
resulting temporary covering, i.e., hiding of objects by other
objects.
As mentioned above, Egenhofer provides a framework for reasoning about
topological relations. Work on qualitative reasoning for directions
has been done by Frank (Frank (1991)). Hernandez
(Hernández (1991)) gives an account for both, topological and
directional reasoning. None of these approaches deals with possibly
graded applicabilities of spatial relations or coverings of objects.
Thus, in order to exploit applicability degrees on the level of base
relations and to cope with coverings of objects, these approaches will
have to be extended.
Our intention is to develop an integrated approach for directional
and topological relations in order to provide natural language
access to visual data on the basis of a 3-dimensional geometric
representation.
In our talk we will show how to put together the various building
stones of related and previous work for the directional and
topological relations. In addition, we will present first results on
the unified inference mechanism for spatial reasoning about both
types of relations.
References
- M. Bierwisch.
Semantische und konzeptuelle Repräsentation lexikalischer Einheiten. In: R. Ruzicka, W. Motsch, eds., Untersuchungen zur Semantik. Studia grammatica 22, pp. 61-99, Akademie-Verlag, Berlin, 1983.
- M. J. Egenhofer.
Reasoning about Binary Topological Relations. In: O. Günther, H.-J. Schek, eds., Advances in Spatial Databases, pp. 144-160, Springer, Berlin, Heidelberg, 1991.
- A. U. Frank.
Qualitative Spatial Reasoning with Cardinal Directions. In: H. Kaindl, ed., 7. Österreichische Artificial-Intelligence-Tagung, pp. 157-167, Springer, Berlin, Heidelberg, 1991.
- D. Hernández.
Relative Representation of Spatial Knowledge: The 2-D Case. In: D. M. Mark, A. U. Frank, eds., Cognitive and Linguistic Aspects of Geographic Space, pp. 373-385, Kluwer, Dordrecht, 1991.
- M. Herweg.
Ansätze zu einer semantischen Beschreibung topologischer Präpositionen. In: C. Habel, M. Herweg, K. Rehkämper, eds., Raumkonzepte in Verstehensprozessen: Interdisziplinäre Beiträge zu Sprache und Raum, pp. 99-127, Niemeyer, Tübingen, 1989.
- G. Herzog, T. Rist, E. André.
Sprache und Raum: Natürlichsprachlicher Zugang zu visuellen Daten. In: C. Freksa, C. Habel, eds., Repräsentation und Verarbeitung räumlichen Wissens, pp. 207-220, Springer, Berlin, Heidelberg, 1990.
- E. Lang.
A Two Level Approach to Projective Prepositions. In: G. Rauh, ed., Approaches to Prepositions, pp. 127-167, Narr, Tübingen, 1991.
- E. Lang, K.-U. Carstensen, G. Simmons.
Modelling Spatial Knowledge on a Linguistic Basis: Theory--Prototype--Integration. Springer, Berlin, Heidelberg, 1991.
- J. R. J. Schirra.
Ein erster Blick auf ANTLIMA: Visualisierung statischer räumlicher Relationen. In: D. Metzing, ed., GWAI-89: 13th German Workshop on Artificial Intelligence, pp. 301-311, Springer, Berlin, Heidelberg, 1989.
- P. Wazinski.
Generating Spatial Descriptions for Cross-modal References. In: Proc. of the 3rd Conf. on Applied Natural Language Processing, pp. 56-63, Trento, Italy, 1992.
Gerd Herzog
Last update: Sun Nov 10 00:52:35 MET 1996
Send comments to herzog@acm.org