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Re: Subsetting data

From: Rob Atkinson <rob@metalinkage.com.au>
Date: Sat, 02 Jan 2016 23:46:27 +0000
Message-ID: <CACfF9Lz7zdEEvhM9F_8zzfyiutikLXaQJnJDPnX62DhFewgvug@mail.gmail.com>
To: Peter Baumann <p.baumann@jacobs-university.de>, Simon.Cox@csiro.au, phila@w3.org, public-sdw-comments@w3.org, public-dwbp-comments@w3.org
I share this unease of equating query result with subsets. Maybe there is a
theory which makes this work - but you can generate a query over a
continuous field - maybe thats just a set with an infinite number of
members? Queries can also operate on a set (or subset) and perform
arbitrary functions - you could generate a continuous field from a set of
discrete point observations for example.  If these are "subsets" - then a
statement of the basic theory of what a subset means is needed before the
debate can move (and any useful explanation of the the conclusions can be
shared.)

If not - then there is some set of relationships that need to be named
between separate types of things identified so far in this thread:
1) query (logical)
2) query result (logical - what it means)
3) query endpoint (discovered after URI resolution)
4) query invocation (used to get result)
5) encoded artefact containing query result
6) the set of data being queried
7) logical subsets of data that may be named
8) actual subset retrieved by a query (identifier of a query result)

AFAICT these are all different things - but may be tighly coupled in some
cases: such as a simple query on dimensions of a set - in which case the
logical query can be used as a proxy for most of the other things - but in
other cases these need separate metadata and citation.

How do we handle the simple cases without making the general case an
exercise in ad-hoc overloading or extension of the model?

It doesnt feel to me that there is a neat web-developer-friendly story yet.
The distinctions between different types of things and how they map onto
the Web architecture _and_ the requirements would at least need a worked
example to show how things relate - and this really does mean choosing or
developing an ontology for this. We may decide our expressiveness is
limited to isPartOf  - but that then means that only certain types of
queries make sense - which may be OK but needs explanation. We could point
to set theory and say "at this point we need an ontology to handle these
concepts - this is future work".  I dont think its useful to say "you just
gotta embed some links" - if you look at implementations of Linked Data the
spatial and topological relationships are variable - abusing semantics of
other ontologies ( sameAs especially) - its still the Wild West, after a
heavy night drinking. IMHO the binding of services that support queries
onto sets of data is simply too fundamental a concern to leave
interoperability effectively unsupported.

Cheers
Rob


On Sat, 2 Jan 2016 at 20:17 Peter Baumann <p.baumann@jacobs-university.de>
wrote:

> looking at queries is a nicely general approach (which I like), it is just
> that this transcends subsetting:
> Subset = set of elements which have been preexisting (ex: vectors from a
> vector bundle)
> Query in addition includes
> - fusion = combination of more than one object involved, such as image
> overlay
> - aggregation = delivering scalars, something maybe not in the original
> object (such as a feature bundle, which is not a scalar) -> type change
> - any other type of processing (such as rasterizing vectors, or
> vectorizing rasters) -> type change
>
> Note that this narrow definition of subset includes an OGC WFS / Filter
> Encoding right away, whereas the "extended view" does not.
>
>
> -Peter
>
>
>
> On 2016-01-02 01:10, Simon.Cox@csiro.au wrote:
>
> > to be persistent, identifiers should not include queries against a
> specific API or query endpoint.
>
> For sure. I didn't say anything about the form of the query. It may not
> even look like a query. Opensearch is an obvious model for
> implementation-independent syntax (after all it's just key-value pairs).
>
> However, I do think it is worth keeping the notion of subset=query result
> in view. Sure, some query results may be more persistent and therefore
> worthy of denotation with a special identifier. But the same subset will
> also be the result of some query anyway. That's just an example of
> non-unique identifiers.
>
> Simon J D Cox
>
> Research Scientist
>
> Environmental Information Infrastructures
>
> Land and Water
>
> CSIRO
>
>
>
> E simon.cox@csiro.au T +61 3 9545 2365 M +61 403 302 672
>
>    Physical: Reception Central, Bayview Avenue, Clayton, Vic 3168
>
>    Deliveries: Gate 3, Normanby Road, Clayton, Vic 3168
>
>    Postal: Private Bag 10, Clayton South, Vic 3169
>
> people.csiro.au/Simon-Cox
>
> orcid.org/0000-0002-3884-3420
>
> researchgate.net/profile/Simon_Cox3
>
>
>
>
> ------------------------------
> *From:* Phil Archer
> *Sent:* Friday, 1 January 2016 9:05:25 AM
> *To:* Cox, Simon (L&W, Clayton); public-sdw-comments@w3.org;
> public-dwbp-comments@w3.org
> *Subject:* Re: Subsetting data
>
>
>
> On 30/12/2015 21:26, Simon.Cox@csiro.au wrote:
> > Another way of looking at it is that a query, encoded as a URI pattern,
> defines an implicit set of potential URIs, each of which denotes a subset.
>
> True, but to be persistent, identifiers should not include queries
> against a specific API or query endpoint. That, for me, is the key
> point. OpenSearch provides a model where a query is included in a URL
> that can be considered persistent because there is a layer of
> indirection that could be changed without the URL changing, but a URL
> that includes a SQL or SPARQL query directly must be considered
> ephemeral IMO.
>
> Phil
>
>
> >
> > Simon J D Cox
> > Environmental Informatics
> > CSIRO Land and Water
> >
> > E simon.cox@csiro.au T +61 3 9545 2365 M +61 403 302 672
> > Physical: Central Reception, Bayview Avenue, Clayton, Vic 3168
> > Deliveries: Gate 3, Normanby Road, Clayton, Vic 3168
> > Postal: Private Bag 10, Clayton South, Vic 3169
> > http://people.csiro.au/Simon-Cox
> > http://orcid.org/0000-0002-3884-3420
> > http://researchgate.net/profile/Simon_Cox3
> >
> > ________________________________
> > From: Phil Archer
> > Sent: Wednesday, 30 December 2015 6:31:16 PM
> > To: Manolis Koubarakis; 'public-sdw-comments@w3.org'; Annette Greiner;
> Eric Stephan; Tandy, Jeremy; public-dwbp-comments@w3.org
> > Subject: Subsetting data
> >
> > At various times in recent months I have promised to look into the topic
> > of persistent identifiers for subsets of data. This came up at the SDW
> > F2F in Sapporo but has also been raised by Annette in DWBP. In between
> > festive activities I've been giving this some thought and have tried to
> > begin to commit some ideas to a page [1].
> >
> > During the CEO-LD meeting, Jeremy pointed to OpenSearch as a possible
> > way forward, including its geo-temporal extensions defined by the OGC.
> > There is also the Linked Data API as a means of doing this, and what
> > they both have in common is that they offer an intermediate layer that
> > turns a URL into a query.
> >
> > How do you define a persistent identifier for a subset of a dataset? IMO
> > you mint a URI and say "this identifies a subset of a dataset" - and
> > then provide a means of programmatically going from the URI to a query
> > that returns the subset. As long as you can replace the intermediate
> > layer with another one that also returns the same subset, we're done.
> >
> > The UK Government Linked Data examples tend to be along the lines of:
> >
> > http://transport.data.gov.uk/id/stations
> > returns a list of all stations in Britain.
> >
> > http://transport.data.gov.uk/id/stations/Manchester
> > returns a list of stations in Manchester
> >
> > http://transport.data.gov.uk/id/stations/Manchester/Piccadilly
> > identifies Manchester Piccadilly station.
> >
> > All of that data of course comes from a single dataset.
> >
> > Does this work in the real worlds of meteorology and UBL/PNNL?
> >
> > Phil.
> >
> >
> >
> >
> > [1] https://github.com/w3c/sdw/blob/gh-pages/subsetting/index.md
> >
> >
> >
> >
> > --
> >
> >
> > Phil Archer
> > W3C Data Activity Lead
> > http://www.w3.org/2013/data/
> >
> > http://philarcher.org
> > +44 (0)7887 767755
> > @philarcher1
> >
> >
>
> --
>
>
> Phil Archer
> W3C Data Activity Lead
> http://www.w3.org/2013/data/
>
> http://philarcher.org
> +44 (0)7887 767755
> @philarcher1
>
>
> --
> Dr. Peter Baumann
>  - Professor of Computer Science, Jacobs University Bremen
>    www.faculty.jacobs-university.de/pbaumann
>    mail: p.baumann@jacobs-university.de
>    tel: +49-421-200-3178, fax: +49-421-200-493178
>  - Executive Director, rasdaman GmbH Bremen (HRB 26793)
>    www.rasdaman.com, mail: baumann@rasdaman.com
>    tel: 0800-rasdaman, fax: 0800-rasdafax, mobile: +49-173-5837882
> "Si forte in alienas manus oberraverit hec peregrina epistola incertis ventis dimissa, sed Deo commendata, precamur ut ei reddatur cui soli destinata, nec preripiat quisquam non sibi parata." (mail disclaimer, AD 1083)
>
>
>
>
Received on Saturday, 2 January 2016 23:47:12 UTC

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