SpatialThing and feature (again)

Dear all,

I was having a discussion with a colleague whether the uses of "feature" in ISO 19109, geo:Feature in GeoSPARQL and "feature" in our BP document are consistent. My current conclusion is that they are not consistent, so I raise this here, also to see, if we need to be more clear in the BP text. If someone can point out the error in my analysis, this would be very welcome :)

In the section about "spatial things" and "features" in the BP [1] we basically build on the ISO 19101/19109 feature definition (with the special twist that Spatial Thing covers both "real-world phenomena" and their abstractions like “feature”). Our current definition of Spatial Thing ("anything with spatial extent") seems to imply that these are restricted to real-world phenomena where it semantically makes sense to have a property with a geometry as a value. The use of "Spatial" in the name also implies this.

This is consistent with GeoSPARQL in the sense that there is a standard property geo:hasGeometry for all entities that are a geo:Feature that has a geo:Geometry as its value. My interpretation of this is that this implies that it must be semantically correct for every sub-class of geo:Feature to provide a geometry. (Or is that too strict?)

But GeoSPARQL also states that it uses "feature" as defined in ISO 19101/19109/19156.

However, ISO 19109, which defines the General Feature Model used by ISO/TC 211 and OGC in its standards, does not require that features have a spatial extent or are something where it semantically makes sense to attach a geometry to. Classifying something as a feature is merely a statement of relevance ("the classification of real-world phenomena as features depends on their significance to a particular universe of discourse"), e.g. typically the resources that you would like to access/query in a dataset. One example in ISO 19109 is an application schema where a loan (on a building) is a feature. Many application schemas based on ISO 19109 include similar types of features.

A loan does not have a spatial extent and a has-geometry property does not make sense (to me), so a loan is not a Spatial Thing (in the sense of our BP document) and it also seems wrong to declare it as a geo:Feature.

If the analysis is correct, should we be more clear about this difference in section 5 of the BP (and perhaps the glossary)? 

It would also be good to be more clear about this in the planned revision of GeoSPARQL.

This discussion is somewhat philosophical, but has direct consequences when converting data based on the ISO/OGC "SDI" standards to RDF.

Best regards,


Received on Thursday, 13 April 2017 12:03:54 UTC