Relationship between resources identifying the same real-world phenomenon

[jechterhoff]

Description

In general, but even within the INSPIRE SDI itself, several digital abstractions may and generally will exist for the same real-world phenomenon. The same organisation may manage multiple datasets on different scales. For example, mapping agencies and road authorities both will usually manage data about the road network in separate datasets.

It is important to understand that there is no requirement that only a single URI is used for the real-world phenomenon - it is perfectly fine to use different URIs. Of course, it would be preferable, if only a single URI was used consistently for the same real-world phenomenon, but it would be an organisational challenge to implement the mechanisms and processes for this. It would require significant work in the INSPIRE Member States to establish the necessary governance and infrastructure.

When multiple URIs for the same real-world phenomenon exist and this is known, we propose that this fact is declared using owl:sameAs.

NOTE1: the distinction between the real-world phenomenon and the feature document (for further details, see issue #22) is essential here, because the owl:sameAs would only make the real-world phenomena the same, but not the feature documents.

NOTE2: regardless if a distinction is made between the real-world phenomenon and the feature document: if a feature type has a thematic identifier then it can be used to identify if two objects that are of this feature type describe the same real-world object.

[jechterhoff]

Using owl:sameAs to assert that two URIs identify the same real-world phenomenon should be avoided if there is a chance that OWL reasoning will be applied on the data.

Reasoning might not be a typical use case of linked data applications, but some users might still apply reasoners to analyse the data. In such a situation, the reasoner would treat individuals that are owl:sameAs as equal. Each individual will then also have the property values that the other has. An individual can then have multiple geometries, for example, which can be an issue (which geometry should be used by the application).

In general, owl:sameAs should not be used to model that different individuals/resources represent the same real-world phenomenon. owl:sameAs declares individual equality, i.e. that a list of individuals/resources are equal. Different abstractions of a real-world phenomenon - in other words: features - usually are not equal. They are different "things". They may be similar or related, but not necessarily fully equal. See the paper When owl:sameAs isn’t the Same: An Analysis of Identity in Linked Data for further details.