Database Reference
In-Depth Information
This can be useful for making inferences. For example, given
Medina is the capital city of Merea.
Meddy is the capital city of Merea.
Individual: Medina
Facts: isCapitalCityOf Merea
Individual: Meddy
Facts: isCapitalCityOf Merea
Since we know that isCapitalCityOf can only have one object, then the two objects
we have been given, Medina and Meddy, must be the same thing:
Medina and Meddy are the same thing.
Individual: Medina
SameAs: Meddy
The key property in OWL 2 (
owl:hasKey
) is akin to the idea of a primary key
in a relational database, allowing you to provide a separate identifier (as well as the
URI) for each individual. In practice, this is mostly used to store the primary key
from the database when converting relational data to Linked Data in RDF. As with
relational data, a key can be made up of a set of properties. In OWL, a key property
is not automatically a functional property, that is, the key property may take more
than one value, although you can certainly state that it is functional, if desired.
A statement using the
owl:hasKey
property says that each named instance of
a class is uniquely identified by a (data or object) property or set of properties.
That is, if two named instances of the class have the same value for their key prop-
erty, it can be inferred that they are the same individual. There is no equivalent
statement in Rabbit.
Class: TaxableProperty
HasKey: hasTaxationNumber
This says that each taxable property is uniquely identified by a taxation number.
If we then use Ash Fleet Farm as an example of a taxable property and state that it
has the taxation number 12345,
Individual: AshFleetFarm
Facts: hasTaxationNumber “12345”
and if we then come across another individual with the taxation number 12345, we
can infer that it is Ash Fleet Farm. You can see that this is similar to the impact
of an inverse functional property except that it only applies to individuals that are
explicitly named, and we cannot draw the inference that every individual that has a
taxation number belongs to the class TaxableProperty.
9.3.12 r
efLexivity
Reflexivity means that the relationship holds between a class and itself. For example,
the property part_of is sometimes seen as reflexive.7
7
Therefore, for
any
class that
uses the part_of relationship, it will be possible to say that the class is part of itself:
