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Re: [dxwg] Summary statistics [RSS] (#84)

From: Andrea Perego via GitHub <sysbot+gh@w3.org>
Date: Sun, 17 Feb 2019 14:52:29 +0000
To: public-dxwg-wg@w3.org
Message-ID: <issue_comment.created-464466483-1550415148-sysbot+gh@w3.org>
For spatial / temporal resolution, see [UC15](https://www.w3.org/TR/dcat-ucr/#ID15), which describes the general context and provides the relevant references.

These topics were discussed by the SDW WG, and then with the DWBP WG (in particular, with @aisaac and @riccardoAlbertoni ), which led to a proposal on how to specify it by using DQV. 

The proposal is included as an example (focussing on spatial resolution only) in [DQV, ยง6.13 (Express dataset precision and accuracy)](https://www.w3.org/TR/vocab-dqv/#h-expressdatasetaccuracyprecision), which was in turn re-used into [SDW's Best Practice 14 (Describe the positional accuracy of spatial data)](https://www.w3.org/TR/sdw-bp/#desc-accuracy).

We should therefore re-use and consolidate that approach.

About consolidation, I summarised what I see as issues to be addressed in the context of the possible revisions to GeoDCAT-AP ( see https://github.com/semiceu/geodcat-ap/issues/3).

For our convenience, I copy-paste below the relevant text from https://github.com/semiceu/geodcat-ap/issues/3: 

> Basically, DQV models this information as observations / measurements of a given quality metric (which corresponds to a given type of resolution).
> 
> [...]
> 
> [Adopting] This [solution] would however require the definition of two groups of individuals:
> 1. Those corresponding to the different types of resolution (denoting a quality metric).
> 2. Those corresponding to each of the different levels of resolution (denoting the measurement of a specific quality metric). 
> 
> As far as the first group is concerned (i.e., the different types of resolution), these individuals can be defined in DQV as follows:
> 
> ````turtle
> :SpatialResolutionAsEquivalentScale a dqv:Metric;
>   skos:definition "Spatial resolution of a dataset expressed as equivalent scale,
> 	  by using a representative fraction (e.g., 1:1,000, 1:1,000,000)."@en ;
>   dqv:expectedDataType xsd:decimal ;
>   dqv:inDimension dqv:precision .
>     
> :SpatialResolutionAsDistance a dqv:Metric;
>   skos:definition "Spatial resolution of a dataset expressed as distance"@en ;
>   dqv:expectedDataType xsd:decimal ;
>   dqv:inDimension dqv:precision .
> ````
> 
> This initial list can be further extended. E.g.:
> 
> ````turtle    
> :SpatialResolutionAsHorizontalGroundDistance a dqv:Metric;
>   skos:definition "Spatial resolution of a dataset expressed as horizontal ground distance"@en ;
>   dqv:expectedDataType xsd:decimal ;
>   dqv:inDimension dqv:precision .
>     
> :SpatialResolutionAsVerticalDistance a dqv:Metric;
>   skos:definition "Spatial resolution of a dataset expressed as vertical distance"@en ;
>   dqv:expectedDataType xsd:decimal ;
>   dqv:inDimension dqv:precision .
>     
> :SpatialResolutionAsAngularDistance a dqv:Metric;
>   skos:definition "Spatial resolution of a dataset expressed as angular distance"@en ;
>   dqv:expectedDataType xsd:decimal ;
>   dqv:inDimension dqv:precision .    
> ````
> 
> The question is in which space such individuals should be defined [...].
> 
> The definition of individuals in the second group is however more problematic, since the level of resolution and unit of measurement are arbitrary (1:1000, 1:100, 1m, 1km, 100m, 10 decimal degrees, etc.).
> 
> Possible options include the following ones:
> 
> 1. Define only the individuals corresponding to the types of spatial / temporal resolution, whereas the individuals expressing the actual resolution will be defined at the data level. This solution is not optimal, since it will result in multiple definitions of the same individuals.
> 2. Define individuals only for some levels of resolution and units of measurements - e.g., the most common ones. This solution may address the majority of (but not all) the cases.
> 3. Set up a URI space supporting arbitrary levels of resolution and units of measurements. This register will dynamically generate the corresponding individuals based on information included in their URI.
> 
> An example of the last option, including also a proposal for how these individuals could be defined, is available at:
> 
> http://geodcat-ap.semic.eu/id/resolution/

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