Database Reference
In-Depth Information
10.4.5.1 Symmetric Properties
In Chapter 6, it was shown how Merea Maps could represent a road network using
statements of the form:
Medina is connected to Medina Road.
Individual: Medina
Facts: isConnectedTo MedinaRoad
This just says that Medina is connected to Medina Road, not that Medina Road is
connected to Medina. The following additional statement was required:
Medina Road is connected to Medina.
Individual: Medina Road
Facts: isConnectedTo Medina
This is because in RDFS there is no way to say a property works both ways around,
and as a result we have to produce twice as many assertions as we would like. From
Chapter 9, we have seen that OWL provides a way to make the “is connected to”
property work in both directions. Merea Maps achieves this by stating that the
property is symmetric:
The relationship “is connected to”
is symmetric.
ObjectProperty: isConnectTo
Characteristics: symmetric
Now, it is simply possible to write one or the other of the statements about the con-
nectivity between Medina and Medina Road, and the other is automatically inferred.
10.4.5.2 Inverse Properties
Merea Maps then realizes it not only has a similar issue with “has part,” but also
that it is not quite the same. What it would like to be able to do is only say either
X is a part of Y, or that Y has a part X, and not have to say both statements all the
time. However, this is not identical to the “is connected to” property, and making
“has part” symmetric will not work. This is because the “has part” property has a
distinctly different meaning from “is a part of,” whereas “connected to” worked in
both directions. However, Merea Maps can see that OWL still allows it to do what
it wants by making the property an inverse property rather than a symmetric one as
described in Chapter 9. This is demonstrated in the specific example that follows.
Merea Maps knows that Lower Field is part of Ash Fleet Farm; therefore, Ash Fleet
Farm has a part that is Lower Field. Rather than having to explicitly state both facts,
Merea Maps now just states:
The relationship “part of” is the
inverse of “has part”.
Lower Field is part of Ash Fleet Farm.
ObjectProperty: partOf
InverseOf: hasPart
Individual: LowerField
Facts: partOf AshFleetFarm
Then, the following statement can be inferred:
Ash Fleet Farm has part Lower Field.
Individual: AshFleetFarm
hasPart LowerField
