RE: Does 'Feature' = 'Real World Thing'?

Hi all,

IMO what we call features in the geospatial domain are usually abstractions of representations on maps of real world things; not abstractions of real world things themselves. I see this a lot in information models in the Netherlands. For example, we have two information models that have features of class Building. They both model exactly the same set of objects, but one model captures the building geometry as seen from above, the other from ground level. Different features, same real world thing...

Linda

Van: Jeremy Tandy [mailto:jeremy.tandy@gmail.com]
Verzonden: maandag 19 oktober 2015 8:43
Aan: SDW WG Public List
Onderwerp: Does 'Feature' = 'Real World Thing'?

Hi-

I've been working through the discussion on Linking-Data and this uncovered (or, really, re-found) this issue.

By OGC terminology, Feature is "an abstraction of a real world phenomenon". Linked Data folks like to talk about Real World Things (both physical and abstract).

There's a disjoint here that we need to resolve.

I've captured the question on the wiki [1] and included the content below.

Jeremy

[1]: https://www.w3.org/2015/spatial/wiki/Linking_Data#Question:_is_a_Feature_the_Real_World_Thing.3F


Question: is a Feature the Real World Thing?
ISO 19101 -- Geographic information - Reference model states:
·         [4.11] feature: abstraction of real world phenomena
·         [4.12] feature attribute: characteristic of a feature ...
·         EXAMPLE 2 A feature attribute named ‘length’ may have an attribute value ’82.4’ which belongs to the data type ‘real’.

The definition of feature attribute is clear- it's a piece of information about the feature.

feature is not quite so clear. In this context, what does abstraction mean?

Typically, the Linked Data community refer to Real-world ‘Things’ (see Designing URI sets for the UK public sector<https://www.gov.uk/government/publications/designing-uri-sets-for-the-uk-public-sector>); real-world Things (or just Things) are "are the physical and abstract ‘Things’ that may be referred to in statements". Examples include a school, a road, a person (physical); a government sector, an ethnic group, an event (abstract).

A commonly used example is Manchester Piccadilly Railway Station. A URI for Manchester Piccadilly Railway Station would refer to the real station, constructed from steel and concrete with thousands of people passing through it each day. Clearly one cannot expect an HTTP request to return the real railway station (!); it returns an information object about the railway station.

W3C URLS in Data (FPWD)<http://www.w3.org/TR/urls-in-data/> discusses the need to differentiate between the real Thing and the information resource that describes it. The Publishing Data<http://www.w3.org/TR/urls-in-data/#publishing-data> section provides three strategies for doing so.

In the Geographic Community, the Feature is seen as an information resource - which is, in some way, related to the real-world Thing. INSPIRE (Generic Conceptual Model<http://inspire.ec.europa.eu/documents/Data_Specifications/D2.5_v3.4.pdf>) refers to these resources as Spatial Objects: "abstract representation of a real-world phenomenon related to a specific location or geographical area". It notes that the term is "synonymous with "(geographic) feature" as used in the ISO 19100 series" and, later, talks about versioning the Spatial Objects. Clearly, you can only version the record of information held about a real world Thing, not the Thing itself?

So the question remains: are we identifying real-world Things (both physical and abstract) or information objects that describe them? Once that's decided, we need to get our terminology clear and stick to it!