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

Jeremy,

Unfortunately the W3C reference picks up a couple of phrases from the ISO / OGC General Feature Model and so creates its own ambiguity. The key processes are feature "discernment" and feature "representation". The term "real world objects" has no meaning for us until we discern something (e.g. by sensing)  that is separable from the rest our experience, or "universe of discourse". Feature is therefore a way of referring both to that experience and to some artifact such as data that represents or models it (using scheme, attributes, geometries, etc.). This duality is pretty closely mirrored in our apparent dilemma between identification (e.g. by URI / IRI) and linking (e.g. dereferenceable URL). A feature doesn't need to have a representation, but it does need some way of referencing, naming, or identification so that it can be a part of discourse. Of course this is what abstraction means, an identifiable concept that is asserted (and communicated) to generalize specific experience, e.g. Pothole instead of " what did I just hit?). We implement abstractions with feature data, such as points or linear measures.

What does this mean for spatial data on the Web? Just that we need to make sure that those two relationships that make up a feature can be communicated across the  Web:  identification of discernment and the fact / assertion that some data or other Web artifact represents it. Do we "know" that two features are the same "real world object"? Not really. The lighthouse and the vertical obstruction may appear according to spatial referencing to be collocated. We may even assert in common sense "That's a strange name for a lighthouse," but the abstraction, schema, attributes, geometry, etc. are separate and may be completely different. 

Just as with Web content in general, it might not be necessary in the vast majority of cases to be very explicit about this formalism, but if we leave it to consumers, particularly of the machine variety, to explore murky implications about the "featureness" of spatial data or what it says about what we say about the world, there will be unfortunate consequences in data-driven interactions with that world.



Joshua Lieberman, Ph.D.
Principal, Tumbling Walls Consultancy
Tel/Direct: +1 627-431-6431
jlieberman@tumblingwalls.com

> On Oct 19, 2015, at 02:42, Jeremy Tandy <jeremy.tandy@gmail.com> wrote:
> 
> 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); 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) discusses the need to differentiate between the real Thing and the information resource that describes it. The 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) 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!
> 
> 
>