Database Reference
In-Depth Information
Broadleaved
Scrub Habitat
Coniferous
Woodland &
Scrub Habitat
Mixed
Wo odland Habitat
Grassland Habitat
is contained with
Tall Herb & Fern
Habitat
Wo odland
Heathland Habitat
…
FIGURE 10.10
Part of Merean Nature's Class hierarchy for Habitats.
As indicated, this is a very strong statement to make. It means that the two classes are
the same class, so anything that is classified as a woodland by Merea Maps would also
be classified as such by Merean Nature and vice versa. Also, all the statements made in
the ontology about Merea Maps' Woodland are also true for Merean Nature's Woodland.
Both Merea Maps and Merean Nature make the assertion that Woodlands contain
trees, but they define the class hierarchies leading to trees differently. In the case of
Merea Maps, it has applied the principle that from a topological point of view a tree
is a secondary concept, so it has said nothing about it and made it a direct subclass
of Thing. Merean Nature, on the other hand, does know a bit about trees and so has a
more complex class hierarchy that can be summarized as Thing, Vegetation, Woody
Vegetation, Tree. On the face of it, then, these classes are different; however, because
there is actually no conflict, Merean Nature can also make these classes equivalent
as well. This is due to the fact that no contradictions exist: In both cases, a Tree is
a subclass of Thing, and all that the Merean Nature's hierarchy does is add more
specificity. As important, Merean Nature's domain expert is happy to accept that
Merea Maps is using the concept of tree in the same manner as Merean Nature. It is
also worth considering that if the domain expert had decided that Merea Maps was
using the concept of tree differently, then Merean Nature would probably also come
to the conclusion that the Woodland classes were also not equivalent as both refer to
their respective Tree classes.
An example of where differences certainly occur can be seen if we consider what
happens when the domain expert tries to address whether Lake is used in the same
way in both ontologies. In the Merea Maps ontology, a Lake refers to an open area of
water that has a significant flow; Merean Nature describes a Lake as any area of open
water larger than 2 hectares. There is clearly a relationship between the two, but they
are also not equivalent: There will be certain individual Lakes defined by Merean
Nature that would not be classified as Lake by Merea Maps and vice versa. However,
the domain expert notes that anything that Merea Maps has classified as a pond,
reservoir, or lake that has a surface area of greater than 2 hectares will be classified
as a lake by Merean Nature. The problem is that OWL does not enable someone to
