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Re: Subsetting data

From: Peter Baumann <p.baumann@jacobs-university.de>
Date: Fri, 1 Jan 2016 14:49:33 +0100
To: Phil Archer <phila@w3.org>, Clemens Portele <portele@interactive-instruments.de>, Rob Atkinson <rob@metalinkage.com.au>
CC: Simon Cox <Simon.Cox@csiro.au>, <koubarak@di.uoa.gr>, <public-sdw-comments@w3.org>, <amgreiner@lbl.gov>, <ericphb@gmail.com>, <jeremy.tandy@metoffice.gov.uk>, <public-dwbp-comments@w3.org>
Message-ID: <568683ED.5010505@jacobs-university.de>

On 2016-01-01 10:26, Phil Archer wrote:
> On 31/12/2015 09:33, Peter Baumann wrote:
>> Hi all,
>> there is work already in this realm which might be useful.
>> - Stephan Proell has been working on subset identifiers in the context of RDA.
> That's interesting. Can you put us in touch, please? I'll be engaging more
> fully with the RDA as of now and hope to got to the Japan plenary.
>> - In the context of data/metadata linking there is work on connecting arrays
>> into tables (ie, relational -> ISO SQL/MDA [1]), into hierarchies (ie, XML ->
>> OGC WCPS [2]) and into RDF (have to find the paper). This allows to determine
>> subsets via the resp. query mechanism, which I consider the most general way. As
>> is the case with URLs already, different queries can point to the same result =
>> "subset". Path expressions, as Phil used in his example, is one way of
>> expressing subsets from composite entities.
> This feels like live queries. Nothing wrong with that of course, but I'm
> trying to focus on persistent IDs for 'typical subsets' like 'latest satellite
> image of location X.'
>> Generally, "subsetting" can mean many, many things. In the most basic case it
>> denotes identifying a part of a coverage that is a coverage again: spatial and
>> temporal subsetting in WCS Core, and also range subsetting, ie: extraction of
>> bands/channels/variables from a coverage, resulting in a coverage again. With
>> more general options, this can be trascended - such as retrieving _sets_ of
>> pixels from an image _matrix_. You can replace "coverage" with anything where
>> you wish to maintain some particular properties (array, set uniqueness,
>> hierarchy, closure under a given ontology, ...).
> So you'd bake some dimensions into the URI and they could persist even when
> your great grand child writes WCS Core 27.0 in 2216 ;-)

yes, definitely: Lat, Long, elevation, and time I am convinced will be valid
terminology in 2216 as well ;-)
(at least, we will have well-defined transitions to whatever concepts will be
used then, such as hexagonal horizontal grids)

>> re change of a subset target over time: that is of course always the case, any
>> resource to which a URL points can change so this does not add substantial new
>> problems. A subset may even yield an empty result at some time (such as maybe
>> /UK/Edinburgh or EU/UK at some time ;-) ).
> Indeed, yes.
> Cheers
> Phil
>> re clashes etc: what you are talking about below is not subsetting, but fusion
>> (a "join" or "union"). This is a different mechanism with different rules (cf
>> ontology matching when merging two ontologies).
>> Happy 2016,
>> Peter
>> [1] D. Misev, P. Baumann: /Extending the SQL Array Concept to Support Scientific
>> Analytics/. Proc. Intl. Conf. on Scientific and Statistical Database Management
>> (SSDBM'2014), June 30 - July 2, 2014, Aalborg, Denmark, paper #10
>> [2] P. Baumann: The OGC Web Coverage Processing Service (WCPS) Standard.
>> Geoinformatica, 14(4)2010, pp 447-479
>> On 2015-12-31 09:07, Clemens Portele wrote:
>>> Rob,
>>> what you describe seems to apply to the dataset (resource) the same way it
>>> would apply to any subset resource. I.e. are you discussing a more general
>>> question, not the subsetting question?
>>> Phil,
>>> a (probably often unproblematic) restriction to the temperature/uk/london or
>>> stations/manchester approach is that there is only one path, so you end up
>>> with limitations on the subsets. If you want to support multiple subsets, e.g.
>>> also stations where high speed trains stop, stations that have a ticket shop,
>>> etc. then there are several issues with a
>>> /{dataset}/{subset}/…/{subset}/{object} approach. These include an unclear URI
>>> scheme ("manchester" and "eurostar" would be on the same path level),
>>> potential name collisions of subset names of different subsetting categories,
>>> and multiple URIs for the same feature/object.
>>> Best regards,
>>> Clemens
>>>> On 31 Dec 2015, at 03:07, Rob Atkinson <rob@metalinkage.com.au
>>>> <mailto:rob@metalinkage.com.au>> wrote:
>>>> I'm not a strong set-theoretician - but it strikes me there are some tensions
>>>> here:
>>>> Does the identifier of a set mean that the members of that set are constant,
>>>> known in advance and always retrievable?   Is a query endpoint a resource
>>>> (does either URI or URL have meaning against a query that delivers real time
>>>> data - including the use case of "at this point in time we think these things
>>>> are members of this set?" )
>>>> If the subset is the result of a query - and you care that it is the same
>>>> subset another time you look at it - are you actually assigning an identifier
>>>> to the artefact - which is the query response, whose properties include the
>>>> original query, where it was made, and the time it was made?
>>>> Can you define an ontology for terms like subset, query, response that you
>>>> all agree on?
>>>> I share Phil's implicit concern that subsetting by type with URI patterns may
>>>> not be universally applicable - IMHO that equates to a "sub-register"
>>>> pattern, where a set has its members defined by some identifiable process
>>>> (indepent of any query functions available) - which may include explicit
>>>> subsets - for example by object type, or delegated registration processes.
>>>> That probably fits the UK implementation better than a query-defined subset.
>>>> If subsets have some prior meaning - and a query is used to access then from
>>>> a service endpint - then the query is a URL that needs to be bound to the
>>>> object URI. AFAICT thats a very different thing to saying an arbitrary query
>>>> result defines a subset of data.
>>>> I think you may, in general, assign an ID to the artefact which is the result
>>>> of a query at a given time, and if you want to make that into something with
>>>> more semantics then you need make it into a new type of object which can be
>>>> described in terms of what it means. I think currently the conversation is
>>>> conflating these two perspectives of "subset".
>>>> Cheers, and farewell to 2015.
>>>> Rob Atkinson.
>>>> On Thu, 31 Dec 2015 at 08:26 <Simon.Cox@csiro.au <mailto: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.
>>>>      Simon J D Cox
>>>>      Environmental Informatics
>>>>      CSIRO Land and Water
>>>>      E simon.cox@csiro.au <mailto: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
>>>>      <mailto:public-sdw-comments@w3.org>'; Annette Greiner; Eric Stephan;
>>>>      Tandy, Jeremy; public-dwbp-comments@w3.org
>>>>      <mailto: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 <http://philarcher.org/>
>>>>      +44 (0)7887 767755
>>>>      @philarcher1

Dr. Peter Baumann
 - Professor of Computer Science, Jacobs University Bremen
   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
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