Re: Requirements for units of measure, accuracy and precision

When this was raised and we asked Phil for guidance, we were basically told
DWBP is pretty much fixed, if we care it behooves us to address it even ifs
its a more general issue. I think we just need to note its a more general
issue, and provide what we feel is a BP otherwise there is really no useful
path to implementation.

Given precision is a first class concern of spatial data - as spatial
resolution is going to be ever critical in the Internet of Things
especially, we need to handle this.  Precision may be common to a dataset
due to a common methodology, specific to a sensor, or time-varying - such
as GPS coordinates. The BP needs to address how to attach this at this
different levels of granularity. We need to cover both measured position
and gridded coverages as well, and preferably not with completely different
approaches. Precision is not generally an attribute of a CRS, unless we are
going to define CRS for every possible grid - and that would be a fairly
major departure from existing practice i suspect.

UoM is a _similar_ case, and not inherently spatial, so i agree it can be
localised to CRS , TRS,  but I see no harm in tying it in to the same
pattern as spatial precision - whats needed is a BP to provide metadata
about values, to meet the hard requirement of spatial CRS and precision,
but its useful to suggest this would be applicable to UoM. Certainly having
a completely different set of patterns for attribution of uom and CRS feels
like sub-optimal practice.

Rob


On Fri, 26 Aug 2016 at 10:09 <Simon.Cox@csiro.au> wrote:

> Ø  The lack of information on units of measure and the apparent lack of
> concern for proper indication of uncertainty in numbers are widespread in
> spatial data and something should definitely be done about that. However, I
> maintain that both problems are more general than spatial data and are
> therefore out of scope for the UCR document. We have tried hard to limit
> the UCR requirements to only spatial data on the web.
>
>
>
> Frans – I agree with this assessment in principle. Should we try to pass
> it back up to the DWBP group?
>
>
>
> Best Practice 7 https://www.w3.org/TR/dwbp/#quality refers off to the
> Data Quality Vocabulary, which may mean they think it is dealt with, but
> I’m not convinced. It’s one more step away from the readers, at least, and
> none of the examples show units of measure, or suggest where they would be
> found. ‘units’ or ‘uom’ does not appear in their document (in the sense
> that we mean, anyway).
>
>
>
> However, this document is still in ‘Working Draft’ status, although it is
> certainly a pretty mature document by now. We could start by making a
> comment on their public list
> https://lists.w3.org/Archives/Public/public-dwbp-comments/ to the effect
> that
>
>
>
> ‘The requirement to know the units of measure for quantitative data (or
> another kind of ‘reference system’ for other kinds of data values) is not
> mentioned in https://www.w3.org/TR/dwbp/. Units are required in order to
> use quantitative data, so the Data on the Web Best Practices should include
> a recommendation on the topic. This affects the following benefit
> categories: Comprehension (C), Processability (P), Reuse (R)’
>
>
>
> But perhaps this is a place where some more formal coordination between
> the groups is warranted?
>
> @phila – has this issue ever been discussed in the DWBP group? A quick
> search of the email archive doesn’t turn anything up.
>
>
>
> --
>
> As a side comment – it is kinda remarkable how this gets overlooked. I
> raised it in the Open Knowledge forum on their Data Packaging/Frictionless
> Data initiative. As soon as I mentioned it there was acceptance that it is
> in scope, but somehow no-one had brought it up until then.
>
>
>
> Simon
>
>
>
> *From:* Frans Knibbe [mailto:frans.knibbe@geodan.nl]
> *Sent:* Thursday, 25 August 2016 10:50 PM
> *To:* SDW WG Public List <public-sdw-wg@w3.org>
>
>
> *Subject:* Requirements for units of measure, accuracy and precision
>
>
>
> Hello,
>
>
>
> In messages
> https://lists.w3.org/Archives/Public/public-sdw-wg/2016Aug/0172.html and
>
> https://lists.w3.org/Archives/Public/public-sdw-wg/2016Aug/0109.html the
> possibility of adding new requirements to the UC&R doc was brought forward.
> Those should be requirements that
>
>
>
> A) the units of measure (UoM) in spatial data should be made clear
>
> B) the precision of spatial data should be made clear
>
>
>
> From the looks of it, those requirements would at least be requirements
> for the BP deliverable.
>
>
>
> The topic was also discussed in the last SSN teleconference
> <https://www.w3.org/2016/08/23-sdwssn-minutes>. I thought it would be
> good to create a separate thread for these related issues.
>
>
>
> I will first repeat my initial response: The requirements are very good
> requirements. The lack of information on units of measure and the apparent
> lack of concern for proper indication of uncertainty in numbers are
> widespread in spatial data and something should definitely be done about
> that. However, I maintain that both problems are more general than spatial
> data and are therefore out of scope for the UCR document. We have tried
> hard to limit the UCR requirements to only spatial data on the web. This
> constraint is specifically mentioned in the section on methodology
> <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#Methodology>.
> If we were to neglect this constraint, then the amount of requirements
> could run out of hand quickly, the decisions on which requirements to
> include or not would become very arbitrary and the deliverable teams that
> are tasked with meeting requirements would inevitably find out that they
> are not in a position to meet the requirements because they are not in
> scope for their work. Of course the deliverable teams will work with
> additional requirements next to the ones mentioned in the UCR document.
> Those additional requirements will be based on general best practices. I
> think the UoM and precision requirements fall in that class.
>
>
>
> That said, perhaps there is a way to shape the requirements in such a way
> that they can be included in the UCR document, without violating the
> spatial scope constraint too harshly. After all, it has been done for other
> requirements too, to be honest.
>
>
>
> Let's start with the UoM requirement (A). I assume that is about the UoM
> of coordinate data only. I think this is already implicitly covered by the
> CRS requirements Linking geometry to CRS
> <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#LinkingCRS>,
> Determinable CRS
> <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#DeterminableCRS>
> and CRS definition
> <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#CRSDefinition>:
> If those requirements are met, it should always be possible to know the UoM
> of coordinates, because the UoM will be part of the CRS definition. Perhaps
> we should be explicit in mentioning that a CRS definition should include an
> indication of UoM?
>
>
>
> As for the requirement B, if we change the wording a bit the requirement
> could be made applicable to spatial data only and therefore be in scope:
>
>
>
> B2) The use of precision that matches uncertainty in coordinate data
> should be facilitated and encouraged
>
>
>
> With this kind of wording I think the BP editors have a fighting chance of
> meeting the requirement.
>
>
>
> Please share your thoughts...
>
>
>
> Regards,
>
> Frans
>