Geoscience Reference
In-Depth Information
- The
operations
related to these entities allow modeling their structure,
functioning and evolution. We can distinguish three main families of operations:
(1) the measurements that allow specifying the properties of objects (for example,
size and density measurement); (2) the functions that allow characterizing the
relationships between objects, whether they concern proximity (in terms of
similarity or genealogy) or interactions (for example, trade, hydrologic flows and
access time); (3) the rules and functions that allow linking an event to a change or
generating a series of successive changes. In a model on the growth of cities, for
example, the evolution of a city population may consequently be formalized from a
differential equation (logistics equation, for example, expressing an exponential kind
of growth when the population is far from the carrying capacity of the city and
slowing down as it approaches it) or from a rule that can be formulated in the
following way: “if the potential of interaction with other cities is of a given
intensity, then the growth rate of the population is so much”.
This categorization has proved fruitful when frequent moves to and fro are made
between the empirical question, the associated information system and the modeling.
Faced with the same empirical question, multiple ontological choices are possible as
a result. For example, let us suppose that we are concerned with the evolution of a
settlement system in the long term and that we want in particular to model the
change from villages to cities. The following two ontologies are possible:
- first case: we consider the existence of two types of objects, cities and
villages, which are then apprehended as two different “things”; each one will be
characterized by
properties
, and we will be able to define
relations
between these
two types of objects, for example, relationships of functional dependency, as well as
operations
, for example in the form of a transformation rule from one type of object
to the other;
- second case: a single object, the settlement unit, is considered, and the
distinction city/village is then understood through the properties of this object: it can
be a property captured directly by a simple attribute with two modalities or several
properties related to quantitative attributes such as the number of inhabitants, the
economic profile, the level of services or the range of exchanges. In the latter case,
the purpose will be to define the operations, usually from recurring rules to
thresholds, which will allow characterizing the city or village property of the
settlement unit.
The researcher will choose one or the other from these ontologies on the basis of
his assumptions on the differences between the objects
city
and
village
and on the
possibilities of transformation from one to the other. If the assumption is that there is
a semantic difference between city and village, with properties and relations
associated with the village being qualitatively different from those associated with
the city, the first case is to be considered. This is, for example, the point of view of
