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Re: AW: [QB] ISSUE-31 (Aggregation hierarchies) Discussion and proposal

From: Dave Reynolds <dave.e.reynolds@gmail.com>
Date: Thu, 28 Feb 2013 17:45:10 +0000
Message-ID: <512F97A6.6020009@gmail.com>
To: Benedikt Kaempgen <kaempgen@fzi.de>
CC: Government Linked Data Working Group <public-gld-wg@w3.org>
Hi Benedikt,

The proposal doesn't provide any definition of levels and so doesn't 
directly relate to xkos:ClassificationLevel.

I do think levels are a very useful concept, also used in QB4OLDAP, but 
feel they are part of the proposed-postponement and was trying to limit 
our ambition here.

I was trying to limit qb:Hierarchy to more or less just the SDMX 2.0 
notion of "hierarchical code schemes" which provide for multiple 
hierarchies over the same set of codes. That allows for general lattices 
(multiple roots, children can have multiple parents) not just taxonomic 
hierarchies so I allowed that in qb:Hierarchy.

The one place I did go beyond SDMX 2.0 is in the notion of 
qb:AggregatableHierarchy. I included that because that's the use case 
that has most common come up. People want to same that, for example, UK 
is made up of England, Scotland, Wales and NI and that simple statistics 
such as directly observed population counts can be aggregated up that 
hierarchy. This would correspond to the combination of 
xkos:coversExhaustively and xkos:coversMutuallyExclusively.


On 28/02/13 17:17, Benedikt Kaempgen wrote:
> Hi Dave,
> interesting, thanks for your suggestion.
> I have not fully understood the concept of a qb:Hierarchy, yet. But that's me, probably.
> I am wondering how your suggestion aligns with the work on XKOS [1] (formerly, ISO extension to SKOS [2]), in particular with the introduction of xkos:ClassificationLevel.
> Best,
> Benedikt
> [1] <https://github.com/linked-statistics/xkos/blob/master/xkos.html>
> [2] <http://www.w3.org/2011/gld/wiki/ISO_Extensions_to_SKOS>
> ________________________________________
> Von: Dave Reynolds [dave.e.reynolds@gmail.com]
> Gesendet: Donnerstag, 28. Februar 2013 12:30
> An: Government Linked Data Working Group
> Betreff: [QB] ISSUE-31 (Aggregation hierarchies) Discussion and proposal
> ISSUE 31 [1] concerns support for hierarchies other than SKOS. I know
> this one is controversial ...
> In Data Cube as it stands then a cube component (qb:ComponentProperty,
> especially a dimension) can be coded using codes from a
> skos:ConceptScheme. This roughly corresponds to the SDMX notion of a
> Concept Scheme [2] where codes are arranged in a parent/child hierarchy.
> The normal skos:narrower/skos:broader relationships are used to express
> such parent/child relationships.
> Often in statistical publishing values will be given for different
> levels in such a concept scheme - e.g. the population statistics for the
> UK as a whole as well as those for each region. Though the value for the
> parent may not simply be the sum of those for its children.
> Especially when dealing with geographic hierarchies some limitations of
> the current approach that have come up in practice, e.g. see [3].
> There are 3 problems here and a non-problem.
> The non-problem is that it is perfectly reasonable to create a
> skos:Concept to represent an geographic region and to use
> skos:narrower[4] to represent a relevant containment hierarchy. That's
> not why ISSUE-31 is on the list.
> The problems are:
> (a) Publishers would like to reuse existing geographic hierarchies
> already published as linked data (e.g. [5]) but where that data uses
> different predicates to represent the hierarchy than skos:narrower.
> (b) The same geographic regions can participate in multiple hierarchies.
> As well as spatial containment there is also administrative containment.
> We can only use skos:narrower for one of these.
> (c) In cases like [3] people also wish to state when the child concepts
> are disjoint so that aggregation might be possible (so long as the
> measures themselves can be aggregated), or more strongly that the parent
> concepts are a disjoint union of the child concepts.
> It is possible to work around (a) by publishing your own skos:narrower
> assertions about the existing published linked data. However, that is
> problematic to keep up to date, may conflict with someone who wants to
> use skos:narrower in a different sense over the same concepts (see b)
> and can be socially/politically problematic.
> Problems like (b) are handled in SDMX through the use of hierarchical
> code schemes [6] which can be used to create multiple different
> generalized hierarchies over the same code list.
> PROPOSAL.  Proposed approach is a vocabulary extension:
> qb:hierarchy (domain: qb:CodedProperty, range: qb:Hierarchy)
>      Indicates a specification of the hierarchy used for coding this
> property (typically a DimensionProperty). Where a skos:ConceptScheme
> exists with appropriate broader/narrower relations then that should be
> used and should be specified using qb:codeList. The qb:hierarchy
> declaration is only need for situations where a suitable
> skos:ConceptScheme is not available.
> qb:Hierarchy (owl:Class)
>      Specifies a hierarchy which can be used for coding. The same
> concepts may be members of multiple hierarchies provided that different
> qb:[narrowing/broadening]Property values are using for each hierarchy.
> qb:AggregatableHierarchy (sub class of: qb:Hierarchy)
>       Indicates a hierarchy in which each parent concept is a disjoint
> union of its child concepts. So that measures such as simple counts
> *may* be aggregated up the hierarchy.
> qb:hierarchyRoot (domain: qb:Hierarchy, range: skos:Concept)
>      Specifies a root of the hierarchy. A hierarchy may have multiple
> roots but must have at least one.[7]
> qb:narrowingProperty (domain: qb:Hierarchy, range: rdf:Property)
>      Specifies a property which relates a parent concept in the hierarchy
> to a child concept. One of qb:narrowingProperty or qb:broadeningProperty
> must be given but it is not necessary to have both. Note that a child
> may have more than one parent.
> qb:broadeningProperty (domain: qb:Hierarchy, range: rdf:Property)
>      Specifies a property which relates a child concept in the hierarchy
> to a parent concept. One of qb:narrowingProperty or
> qb:broadeningProperty must be given but it is not necessary to have
> both. Note that a child may have more than one parent.
> Dave
> [1] http://www.w3.org/2011/gld/track/issues/31
> [2] http://sdmx.org/docs/2_0/SDMX_2_0%20SECTION_02_InformationModel.pdf p.39
> [3]
> https://groups.google.com/forum/#!topic/publishing-statistical-data/3I1-Ix1Hk14/discussion
> [4] I'm using skos:narrower as a shorthand for
> skos:narrower/skos:broader, no slight intended to skos:broader
> [5] http://data.ordnancesurvey.co.uk/.html
> [6] http://sdmx.org/docs/2_0/SDMX_2_0%20SECTION_02_InformationModel.pdf p.96
> [7] This is to match SDMX 2.0 [6] which also supports multiple roots.
Received on Thursday, 28 February 2013 17:45:39 UTC

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