This paper explores the role of the traditional computational metaphor in our thinking as computer scientists, its influence on epistemological styles, and its implications for our understanding of cognition. It proposes to replace the conventional metaphor --- a sequence of steps --- with the notion of a community of interacting entities, and examines the ramifications of such a shift on these various ways in which we think.

Current geographic information systems (GISs) have been designed for querying and maintaining static databases representing static phenomena and give little support to those users who wish to represent dynamic information or incorporate temporality into their studies. In order to integrate phenomena that change over space and time in GISs, a better understanding of the underlying components of change and how people reason about change is needed. This paper focuses on a qualitative representation of change. It offers a classification of change based on object identity and the set of operations that either preserve or change identity. These operations can be applied to single or composite objects and combined to express the semantics of sequences of change. An iconic, visual language is developed to represent the various types of change and applied to examples to illustrate the application of this language. Such a formalization of the basic components of change lays the foundation for a new generation of formal models that captures the semantics of change and leads to improved interoperability between GISs and process models or simulation software.

Human cognition makes extensive use of visualization and imagination. As a first step towards giving a robot similar abilities, we have built a robotic system that uses a perceptually-coupled physical simulator to produce an internal world model of the robot's environment. Real-time perceptual coupling ensures that the model is constantly kept in synchronization with the physical environment as the robot moves and obtains new sense data. This model allows the robot to be aware of objects no longer in its field of view (a form of "object permanence"), as well as to visualize its environment through the eyes of the user by enabling virtual shifts in point of view using synthetic vision operating within the simulator. This architecture provides a basis for our long term goals of developing conversational robots that can ground the meaning of spoken language in terms of sensorimotor representations.

The paper presents a framework for the formulation and testing of ontological theories embodied in human cognition, concentrating primarily on the domain of geographic categories. Evidence for and against alternative theories of cognitive categories, for example on the part of E. Rosch and her associates, has been hitherto based primarily on studies of categorization of entities of table-top space (pets, tools, fruits). We hypothesize that the structure of our categories does not remain constant as we move from categories of objects at manipulable scales to geographic categories such as nation, mountain, river. More precisely: Geographic objects are not merely located in space, they are tied intrinsically to space in such a way that they inherit from space many of its structural (mereological, topological, geometrical) properties. Categorization in the geographic world is often size- or scaledependent (consider: pond, lake, sea, ocean), and to a much greater extent than in the world of tabletop space, the realization that a thing or type of thing exists at all in the geographic world may have individual or cultural variability. Geographic objects are in very many cases the products of delineation within a continuum, and the boundaries of such objects are themselves highly salient phenomena for purposes of categorization. A battery of experiments is described to test these hypotheses and to serve as a basis for more detailed ontological theorizing. 1.

We discuss an approach to a theory of physical objects and present a logical theory based on a fundamental distinction between objects and their substrates, i.e. chunks of matter and regions of space. The purpose is to establish the basis of a general ontology of space, matter and physical objects for the domain of mechanical artifacts. An extensional mereological framework is assumed for substrates, whereas physical objects are allowed to change their spatial and material substrate while keeping their identity. Besides the parthood relation, simple self-connected region and congruence (or sphere) are adopted as primitives for the description of space. Only threedimensional regions are assumed in the domain. This paper is a revision and slight modification of [Borgo et al. 1996]. 1.

The paper begins with the question "Do mountains exist?" It shows that providing an answer to this question is surprisingly difficult, and that the answer which one gives depends on the context in which the question is posed. Mountains clearly exist as real correlates of everyday human thought and action, and they form the archetype for geographic objects. Yet individual mountains lack many of the properties that characterize bona fide objects, and mountains as a category also lack many of the properties that characterize natural kinds. In the context of scientific modeling of the environment, especially of such phenomena as surface hydrology and fluvial erosion and deposition, mountains are not picked out as constituents of reality in their own right at all; rather they are just parts of the field of elevations whose gradients direct the direction of runoff and influence the intensity of erosion. While an object-based ontology of mountains and other landforms is thus required to do justice to our everyday conceptions of the environment, topographic databases designed to support environmental modeling can be field-based at geographic scales. Where objects are needed to model surface processes these tend to be much smaller, typically individual pebbles or sediment grains, plus occasionally individual organisms or built structures.

When modelling a domain, it is often the case that certain individuals are represented as belonging to multiple categories, generating therefore "tangled " hierarchies: 1. A physical object can be seen as an amount of matter 2. A hole can be seen as a region of space

Ontology is a burgeoning field, involving researchers

After briefly discussing the relevance of the notions "computation" and "implementation" for cognitive science, I summarize some of the problems that have been found in their most common interpretations. In particular, I argue that standard notions of computation together with a "state-to-state correspondence view of implementation" cannot overcome difficulties posed by Putnam's Realization Theorem and that, therefore, a different approach to implementation is required. The notion "realization of a function", developed out of physical theories, is then introduced as a replacement for the notional pair "computation-implementation". After gradual refinement, taking practical constraints into account, this notion gives rise to the notion "digital system" which singles out physical systems that could be actually used, and possibly even built.

A suitable project for the new Millenium is to radically reconfigure our image of human rationality. Such a project is already underway, within the Cognitive Sciences, under the umbrellas of work in Situated Cognition, Distributed and Decentralized Cognition, Real-world Robotics and Artificial Life. Such approaches