Global Positioning System Reference
In-Depth Information
Example
1. The following geographic class of name
Municipality
:
Municipality =
< {
identity
:
String
;
councilHead
:
String
,
countryCode
:
Integer, inhabitant
:
String, area
:
Integer
}, {
point, polygon
} > is defi ned by a set of alphanumeric
attributes (i.e., identity, councilHead, countryCode, inhabitant, area) and
a set of geometric types (i.e., point, polygon).
A
geographic knowledge base
is essentially a set of geographic classes
where each class is identifi ed by a name, and every name is associated with
a class expression (i.e., there are no dangling class names). It is characterized
by an ontology, where the geographic classes can be related by different
types of relationships, e.g.,
Is-A
or
Part-of
. In particular, according to these
mentioned relations, an ontology of a geographic knowledge base can be
organized as a
Is-A
hierarchy or as a
partition
hierarchy as well (Pourabbas
2003; Pourabbas and Rafanelli 2003). The former indicates the well-known
is-a
relationship, and the latter captures the
is-in
relationship or
inclusion
property.
In the literature, basically, three different kinds of semantics for
inclusion have been identifi ed:
class
,
meronymic
, and
spatial
(Storey 1993;
Winston et al. 1987). Class inclusion
7
is the standard subtype/supertype
relationship which has been widely discussed in the database literature, and
it is indicated by
Is-A
(Codd 1979; Tsichritzis and Lochovsky 1982; Teorey
et al. 1986). Concerning meronymic (
Part-whole
, or
Part-of
) inclusion, many
studies have been carried out. One of the various semantics of meronymic
relationships discussed in Storey (1993) is the
place-area
. It concerns parts
which are similar to whole, and they cannot be separated (for instance, the
reception area is part of an offi ce). Finally, the semantics of spatial inclusion
differs from place-area in that it represents objects that are surrounded by
others but they are not part of them (as for instance, car
is-in
city).
We consider the place-area semantics for the inclusion relationship that
is more suitable for capturing the meaning of inclusion in the geographic
context and, in particular, of geographic classes organized as partition
hierarchies (Storey 1993). Furthermore, we can apply the information
content approach of Lin, which is conceived for
Is-A
hierarchies, to partition
hierarchies by using the place-area semantics. Henceforth, for the sake of
simplicity, we will use terms
Is-A
and
Part-of
hierarchies to mean these
kinds of hierarchies.
As highlighted in (Storey 1983), class inclusion is easily confused with member-collection
relationships (as well as other meronymic relationships) because both involve membership
of individuals in a larger set. Meronymic relationships are determined on the basis of
characteristics that are extrinsic to the individual members themselves. Class inclusion is
determined by similarity to other members based on an intrinsic characteristic.
7
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