Database Reference
In-Depth Information
Once this is done, we can now describe Place as follows:
Every Place is a kind of Feature.
Every Place has part a Feature
that is intended for a Purpose.
Every Place is intended for a
Purpose.
Class:Place
SubClassOf: Feature, (hasPart
some Feature that isIntendedFor
some Purpose), isIntendedFor
some Purpose
The main difference is that we now do not have to add the axiom Every Place is
intended for a Purpose; the Purpose is now inferred from the Purpose of the Part.
The one downside is that as this relationship is now inferred, it is not explicit in
the description of Place.
Another potential area where property chains are used is when considering the
footprint of a complex object that is comprised of other features, for example, a farm
that comprises the buildings, fields, farmyard, and so on. By specifying the following
property chain,
Everything that has a Part that
has a Footprint will also have
that Footprint.
ObjectProperty: hasPart
ObjectProperty: hasFootprint
SubPropertyChain:
hasPart o hasFootprint
the footprint of the main feature now comprises all the footprints of the parts that
make it up, so there is no need to specify a separate footprint for the main feature. Of
course, this only works if we are happy to deal with the fact that we have to sum all
the component footprints if we want to work out the area and total extent of the main
feature, and this may introduce complexity elsewhere that we do not really want (since
the ontology will not specifically tell us to sum the footprints, we will merely have
inferred a Feature that has a number of different footprints belonging to it). Again, only
you will know whether the use of property chains is useful for your specific situation.
10.4.6 D
ealing
with
v
agUeness
anD
i
mprecision
,
the
p
roBlems
of
r
oUgh
g
eography
Geography is not the only area that experiences vagueness and imprecision in terms
of both the classes and the measurements associated with the individuals described
by the classes, but it does provide some excellent examples. We shall look at how
Merea Maps addresses two examples of this: imprecise distinctions between classes
and handling geographic features that either do not have well-defined boundaries or
where these boundaries are unknown or imprecisely known. Before discussing these
examples in detail, it should be understood that because of the nature of these prob-
lems, there are no perfect solutions that completely resolve the issues. It is not a case
of completely solving the problems; it is one of better managing them.
10.4.6.1 Imprecision: When Does a Stream Become a River?
The vocabularies of natural languages are littered with terms that are imprecisely
defined and applied in inconsistent ways. Rivers and streams provide an excellent
