Database Reference
In-Depth Information
10.4.5.3 Transitive Properties
Having defined “has part” to be an inverse property, Merea Maps then realizes that
it can further enrich “has part” by making it transitive, although at first little real-
izing the implications. A field that is part of Ash Fleet Farm, which in turn is part of
Ash Fleet Farm Estate, is obviously also part of Ash Fleet Farm Estate. Merea Maps
supports this inference by making its “has part” property transitive:
“has part” is a relationship.
The relationship “has part” is
transitive.
ObjectProperty: hasPart
Characteristics: Transitive
However, in doing so any query that asks “What are the parts of Ash Fleet Farm
Estate?” will get back everything, not just its immediate components: the Farm and
Ash Fleet House. This is a bit like asking what makes up a car and getting every
component down to the last nut and bolt back, rather than just the major elements,
such as the chassis, wheels, engine, body, and so on. There are occasions when get-
ting back a complete component list is what is desired, but more often than not this is
not what is required. To some extent, this can be mitigated by specifying particular
class types in a SPARQL query so that the query does not return things that belong
to class types referring to low-level parts, but this could get a bit messy and may not
always be possible. The transitive restriction is a very blunt weapon. Merea Maps
wants both the ability to return all components and just those that are the immediate
subcomponents of a Feature. They are able to do this by devising a subproperty of
“has part” that is not transitive:
The relationship “has direct
part” is a special type of the
relationship “has part”.
ObjectProperty: hasDirectPart
SubPropertyOf: hasPart
The trick here is that only domain and range restrictions are inherited; hence,
“direct has part” is not transitive, even though its parent property is.
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Merea Maps
then uses this subproperty rather than “has part” as follows:
Ash Fleet Farm Estate has direct
part Ash Fleet Farm.
Ash Fleet Farm has direct part
Lower Field.
Ash Fleet Farm has direct part
Meadow Cottage.
Ash Fleet Farm Estate has direct
part Ash Fleet House.
Individual: AshFleetFarmEstate
Facts: hasDirectPart AshFleetFarm
Individual: AshFleetFarm
Facts: hasDirectPart LowerField
Individual: AshFleetFarm
Facts: hasDirectPart MeadowCottage
Individual: AshFleetFarmEstate
Facts: hasDirectPart AshFleetHouse
Now asking “What are the direct parts of Ash Fleet Farm Estate?” will only
return Ash Fleet Farm and Ash Fleet House, not the field or cottage. Someone is still
able to ask, “What are all the components of the Estate?” by using the “has part”
property in the query rather than “direct has part.” This technique can be applied
wherever there is a need to “switch off” the transitive restriction and will of course
work for all other OWL property restrictions, such as “is connected to” as well.
